Perceptualand Motor Skills, 1991, 72, 183-192. Q Perceptual and Motor Skills 1991
LINGUAL VIBROTACTILE THRESHOLD SHIFT DURING MAGNITUDE-ESTIMATION SCALING: EFFECTS O N MAGNITUDE-ESTIMATION RESPONSES AND SCALING BEHAVIOR ACROSS AGE ' DONALD FUCCI
LINDA PETROSINO
Ohio University, Athens, Ohio
Bowling Green Slate University Bowling Green, Ohio
SUSAN B. SCHUSTER AND ELIZABETH RANDOLPH Ohio Uniuersiiy, Athens, Ohio Summary.-The purpose of this study was to investigate the effects of age on tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Relationships of the Lingual vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were explored. Three groups differing in mean age participated in this study (Group 1 8.05 yr., Group 2 19.46 yr., and Group 3 56.2 yr.). Each subject performed two rnagnitude-estimation tasks. In one task, threshold of sensitivity was measured after every suprathreshold numerical response of the subject. If a threshold shift was recorded, threshold was allowed to return to the pretest baseline level continuing to the next suprathreshold stimulus presentation. The results showed that threshold shift during magnitude-estimation scaling took place for all three age groups and that the shiFt was related to the intensity of the suprathreshold vibratory stimulus being applied to the tongue. They also showed that Group 2 (young adults) performed magnitude-estimation scaling differently when threshold shift was controlled than when it was not. The other two groups of subjects were not similarly affected.
Psychophysical study of the tactile sensory system has been conducted at both threshold and suprathreshold levels through the use of vibratory
stimuli. Threshold investigation has provided information about the sensitivity of the receptor mechanism, and suprathreshold investigation has increased the understanding of the behavior of the tactile sense above the peripheral level of detectability. Recently a series of studies have been conducted which have addressed possible relationships between threshold and suprathreshold tactile function. These studies have looked at the effects of thIeshold shifts occurring during magnitude-estimation scaling (Fucci, Petrosino, Harris, Randolph-Tyler, & Wagner, 1989; Fucci, Petrosino, Schuster, & Wagner, 1990; Fucci, Petrosino, & Wagner, 1789). The effects of aging on thresholds of detection for the sense of touch have been studied in detail (Crary, Fucci, & Bond, 1781; Curtis & Fucci, 1983; Fucci, Petrosino, & Robey, 1982; Petrosino, Fucci, & Robey, 1782; 'Request reprints fmm Dr. Donald Fucci, School of Hearing and Speech Sciences, Ohio University, Athens, O H 45701.
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Verrillo, 1977, 1980). In general, research has shown that tactile thresholds derived from various body locations show a decrease in sensitivity with an increase in age. Aging effects with regard to suprathreshold tactile stimuli have also received some attention (Fucci & Petrosino, 1983; Fucci, Petrosino, Harris, & Randolph-Tyler, 1987; Verrillo, 1982). This research has shown that there is an aging effect for suprathreshold stimulus presentations to various body sites just as there is for tactile threshold of sensitivity. The purpose of the present experiment was to investigate three age groups with regard to tactile sensory system function by studying the effects of tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Relationships of these lingual vibrotactile threshold shifts to suprathreshold-stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were evaluated for each of the three age groups studied.
METHOD Subjects Three groups of subjects participated in this study. The first group, 12 girls and 8 boys, ranged in age from 6 to 9 years (M age = 8.05 yr.). The second group, 12 women and 12 men, ranged in age from 18 to 22 years (M age = 19.46 yr.). The third group, 10 women and 10 men, ranged in age from 50 to 69 years (M age = 56.2 yr.). All subjects had normal speech and hearing and were screened (by interview) for the presence of medical or physical conditions which could have interfered with test results. Apparatus The vibrotactile stimulus-control unit included a sine-wave generator, an experimenter-controlled variable attenuator, a riselfall gate, two universal timers, an audioamplifier, a power amplifier, and an electromagnetic rninivibrator with a probe-contactor extension. The pulsed vibratory signal generated had a frequency of 250 Hz, a 50% duty cycle (on 500 msec. and off 500 msec.) and a rise-fall time of 50 msec. The vibrotactile stimulusmeasurement unit included an accelerometer, a cathode follower, a rnicrophone amplifier, and a voltmeter. The auditory-masking unit consisted of a masking generator and TDH-49P headphones. The masking unit was used to present a narrow band of noise centered around 250 H z at 70 dB H T L bilaterally. A detailed description of the vibrotactile equipment and procedures can be found in a review by Harris, Fucci, Petrosino, and Wallace (1986). Procedure Each subject completed a series of two lingual vibrotactile magnitude-estimation scaling tasks, which were conducted in separate test sessions scheduled one week apart (Stevens, 1955). For both scaling tasks, the subject
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was seated in an adjustable chair and positioned so that the tongue could be placed against the bottom of a rigidly mounted plastic disk. A hole in the center of the disk provided access for the probe-contactor extension of the vibrator to the anterior midline section of the dorsum of the tongue. The contactor on the end of the probe had an area of ,128 cm2 and there was a 1-mm gap between the contactor and the disk. The TDH-49P headphones were placed over the subject's ears for binaural auditory masking of the 250-Hz vibrotactile stimulus being applied to the tongue. An ascending method of limits was used to obtain threshold of sensitivity for all subjects prior to each of the two magnitude-estimation tasks (Hall, Fucci, & Arnst, 1972). This method of threshold testing was chosen over the forced-choice criterion-free method of threshold testing to minimize subjects' fatigue and sensory-system adaptation (Petrosino & Fucci, 1983). Accepted threshold was the mean of three successive readings within a 5-mV range (Telage & Fucci, 1974). These obtained thresholds were necessary so the suprathreshold intensities for magnitude estimation could be set in reference to each subject's threshold of sensitivity (Verrillo, Fraioli, & Smith, 1969). They were also necessary in this experiment for determination of threshold shift and for the return of threshold to baseline in the second magnitude-estimation scaling task. During the first lingual vibrotactile magnitude-estimation task, each subject was required to assign numbers to a series of pulsed 250-Hz vibrotactile stimuli at eight randomly presented stimulus-intensity levels, ranging from 6 to 40 dB SL (6, 10, 16, 20, 26, 30, 36, and 40 dB SL). The subject was required to feel the pulsed, 250-Hz stimulus on the tongue for 15 sec. before being required to provide a numerical response. The subject was instructed to think of a number that matched the strength of the vibration felt on the tongue. Whole numbers, decimals, and fractions were indicated as permissible selections (Zwislocki & Goodman, 1980). The subjects were encouraged to be spontaneous in selecting numbers and to make judgments at each stimulus-intensity without reference to those previously presented. After each recording of the subject's verbal numerical response, the tongue was realigned with the probe-contactor extension of the vibrator in preparation for the subsequent stimulus presentation. For each group, the geometric means of the subjects' numerical responses to a single run of each of the eight stimulus intensities were taken as the mean lingual vibrotactile magnitude-estimation responses for that group. The variabhty of subject numerical responses was not calculated. Geometric means are designed to account for extreme score values in either direction from the mean. They are used for statistical summarization of magnitude-scahng data which will often show large differences in the actual numerical responses provided (Petrosino, Fucci, & Harris, 1985).
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During the second scaling task, lingual vibrotactile magnitude-estimation scaling was conducted in a manner similar to that described for the first sealing task, with two procedural changes. First, immediately after the subject provided a verbal numerical response to the 15-sec. presentation of the pulsed, 250-Hz stimulus at one of the eight intensities, lingual vibrotactile threshold of sensitivity was rechecked using the threshold technique described above. This postmagnitude-estimation response-threshold determination allowed the experimenter to assess threshold shift resulting from the suprathreshold-stimulus presentation. Second, if threshold shift was detected, the experimenter performed subsequent threshold checks until threshold returned to the prescaling baseline sensitivity level, before continuing to the next suprathreshold-stimulus presentation. In this manner, the experimenter was assured that each subsequent suprathreshold-stimulus presentation was initiated with the subject's threshold at the prescaling baseline. Postmagnitudeestimation response-threshold determinations were conducted for each of the eight randomly presented suprathreshold-stimulus presentations. Lingual vibrotactile threshold shifts for each subject at each of the eight suprathreshold-stimulus intensities were recorded in decibels sensation level and averaged for each group. The geometric means of each group's numerical responses to a single run of each of the eight stimulus-intensities were taken as the mean responses for the second scaling task (Petrosino, Fucci, & Harris, 1985). A counterbalanced technique was utilized to control for possible learning effects with regard to the lingual vibrotactile scaling tasks. Half of the subjects in each group performed the first scaling task during the first test session and the second scaling task during the second test session conducted one week later. The remaining subjects in each group performed the second scaling task during the first test session and the first scaling task during the second test session conducted one week later.
I t can be seen in Fig. 1 that threshold shift occurred for all three groups of subjects for each of the eight suprathreshold stimulus intensities employed in the magnitude-estimation scaling task on which a threshold check was conducted after each subject's numerical response. A two-factor, mixed design analysis of variance with repeated measures on one factor was performed on the threshold-shift data (Barcikowski, 1983; Bock, 1975). No significant differences among the groups were noted (p = .06). The children, young adults, and older individuals tested performed similarly with respect to threshold shift that occurred during magnitude-estimation scaling. The threshold-shift data for all groups combined, showed a strong relationship between the amount of threshold shift occurring and stimulus intensity
AGE AND LINGUAL VI13ROTACTILE THRESHOLD SHIFT
187
( p < .001). Amount of threshold shift showed a consistent increase with an increase in stimulus intensity. An analysis of variance of three-factor, mixed design with repeated measures on two factors was performed on the magnitude-estimation scaling data (Barcikowski, 1983; Bock, 1975). Over-all differences were found among the three groups of subjects. The three groups performed differently on the scaling tasks with regard to the eight stimulus intensities for both test conditions (where threshold checks were not made and where threshold checks were made) ( p = .02). Post hoc testing using Paired Comparisons indicated that the group of subjects comprised of children (Group 1) performed differently on the scaling tasks with regard to the eight stimulus intensities for both test conditions than the group of subjects comprised of young adults (Group 2) and the group of subjects comprised of older individuals (Group 3). Groups 2 and 3 performed similarly on the scaling tasks for both test conditions. A linear trend analysis indicated that as intensity was increased, the numerical magnitude-estimation responses for atl three groups of subjects increased in a linear fashion (p = .03).
-
Threshold Shift -
0= 0=
Group 1(Age Range 6-9) Group 2 (Age Range 18-22) = Group 3 (Age Range 50-69)
I
I
I
I
I
Stimulus Intensity Levels (dB SL) FIG.1. Threshold shift on the tongue, for three age groups, as a function of suprathreshold stimulus intensity
All three groups of subjects combined did not perform the magnitudeestimation scaling tasks differently for the test condition where threshold checks were not made as opposed to the condition where threshold checks were made ( p = .12). A three-way interaction (p = .02, for groups, conditions, intensities) prompted further testing in which a two-factor mixed design with repeated measures on one factor was performed on each group separately
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(Barcikowski, 1783; Bock, 1775). A difference was found in the magnitude-estimation responses of the young adults for the two scaling conditions ( p = .006). Mean lower and upper power function exponents were derived for each group of subjects for the two scaling tasks employed in this experiment. The exponents are reported in terms of intensity (VerriUo & Chamberlain, 1972). It appears that lingual vibrotactile magnitude-estimation scales may show a limitation in magnitude growth functions around and above 25 dB SL. Harper and Stevens (1753) hypothesized that for certain continua, an "upper threshold" may exist and that above this region, increases in stimulus values show no corresponding gradations in subjective magnitude. The present magnitude-estimations for the three groups reflected such an asymptotic growth function and are consistent with previous research (Fucci, Harris, & Petrosino, 1784; Petrosino, Fucci, & Harris, 1785, 1787). The mean exponents for the lower functions for Group 1, were .58 for the scaling task on which no threshold checks were made, and .56 for the scaling task on which threshold checks were made. The mean exponents for the upper functions for Group 1, were .35 for the no-threshold-check condition, and .45 for the threshold-check condition. For Group 2, the mean exponents for the lower functions were .58 for the no-threshold-check condition, and .54 for the threshold-check condition. The mean exponents for the upper functions for Group 2 were .16 for the no-threshold-check condition and .21 for the threshold-check condition. For Group 3, the mean exponents for the lower functions were .62 for the no-threshold-check condition, and .52 for the threshold-check condition. The mean exponents for the upper slopes for Group 3 were .17 for the no-threshold-check condition, and .14 for the threshold-check condition. A one-factor multivariate analysis of variance performed on the power function data indicated that there were no significant differences among the three groups of subjects for the lower power functions for the two magnitude-estimation scaling conditions (p = .82; p = .78) (Barcikowski, 1983; Bock, 1775). There were significant differences among the three groups of subjects for the upper power functions for both scaling conditions (p = .005; p = .024). Post hoc testing using paired comparisons indicated that the Group 1 subjects provided upper power functions for both test conditions that were statistically different than those of the other two groups of subjects. The young adults and older individuals provided both lower and upper power functions that were statistically similar for both test conditions.
D~scussro~ The results of this study indicate that threshold shift can occur for different age groups during lingual vibrotactile magnitude-estimation scaling when a 250-Hz stimulus of 15 sec. duration is employed. They further show
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that the amount of threshold shift is directly related to the intensity of the suprathreshold stimulus. The threshold shifting that occurred in this study was statistically similar for the three different age groups employed (Fig. 1). The numerical responses of the young adult subjects (Group 2) to the suprathreshold stimulus intensities appear to have been influenced by the threshold shifts that occurred during the magnitude-estimation scaling tasks. The numerical responses of the children (Group 1) and the older individuals (Group 3) did not appear to be similarly influenced by threshold shifts. The young adult subjects consistently provided higher numerical responses at each of the eight suprathreshold intensities for the task in which threshold was allowed to return to prescaling baseline than they did for the task in which possible threshold shift was not determined or controlled during the scaling procedure. It is possible that the young adults were using threshold of sensitivity as a reference for their scaling behavior and that they used this reference differently when it was free to vary as opposed to when it was controlled and set at baseline levels for each suprathreshold stimulus presentation. A reference standard was deliberately not employed in the scaling procedure (Hellrnan & Zwislocki, 1963). Informal questioning of the young adult subjects after testing was completed indicated that most of them had been using an internal referent of their own during magnitude-estimation scaling. The most likely chosen referent was what the subjects thought to be the weakest vibratory sensation that they could feel on their tongues. When the cMdren were asked how they dealt with the scaling procedure they, as a group, were more prone to suggest that they just provided numbers that matched the intensities that they were feeling on their tongues. They did not seem to be using a reference of any kind during the magnitude-estimation scaling. It has been suggested that children, unlike adults, do not have fully formulated internal numerical references (Zwislocki & Goodman, 1980). The older group of individuals (Group 3), like the children, did not feel that the threshold concept was very important to the scahng process. The older group of individuals appeared to be more cautious during the entire testing procedure and wanted more external input from the experimenter as to whether they were performing the task appropriately. It is known that the natural aging process leads to a more "cautious" response behavior in formal testing situations (Aiken, 1980; Hull, 1978; Welford, 1980). The Group 3 subjects appeared to be looking for an external referent to be provided by the experimenter. The children, as a group, performed differently than the other two groups of subjects with regard to the magnitude-estimation scaling for both the no-threshold-check and the threshold-check conditions. More specifically, they provided different sets of numerical responses to the upper four stimulus intensities than the other two groups. This finding can be seen with
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regard to the mean upper power function exponents (reported above), which were much higher for the children than they were for the young adults and older individuals. The children, although their scaling responses showed some degree of asymptotic behavior, came closer to a scaling function that was a straight line throughout the entire range of the eight stimulus intensity levels employed. This kind of scaling behavior in children has been noted in previous studies (Fucci & Petrosino, 1983; Fucci, Petrosino, Harris, & Randolph-Tyler, 1987). It appears that children approach the scaling task differently. They show little caution and provide numbers that do not relate to a particular reference value whether it be threshold of sensitivity or some other numerical set. The results of this study suggest that during magnitude-estimation scaling, shifts in threshold of sensitivity take place that relate to the amount of intensity of the suprathreshold vibratory stimulus being applied to the tongue. This appears to be the case for groups representing different age ranges. These threshold shifts appeared to have an influence on magnitude-estimation scaling results for the group representing young adults, but did not appear to influence scaling results for the groups representing children and older individuals. These two groups of subjects did not seem to relate what was happening at the sensory detection level to the scaling tasks by showing less concern for the need to have an internal referent to relate their numerical responses to. The children appeared to find the magnitude-estimation tasks easy to perform and readily provided numbers anchored only to what they were feeling on their tongues. The older individuals showed a large degree of concern about the scaling tasks, but looked more toward external guidance than a steady internal referent they were using. Threshold shift is an activity that can occur during vibrotactile magnitude-estimation scaling, even when the stimulus involved is of minimal duration and intensity. Threshold shift should be a recognized activity that can influence the suprathreshold numerical responses subjects provide. The results of this particular study suggest that threshold shift has the greatest influence on suprathreshold scaling for individuals who would be classified as young adults. Researchers involved in magnitude-estimation scaling research should be aware of the possibility that threshold shift might influence suprathreshold scaling activities and that age is a possible factor as to the extent of that influence. REFERENCES
AIKEN,L. R. (1980) Problems in testing the elderly. Educational Gerontology, 5, 119-124. BARCIKOWSKI, R. (1983) Computer packages and research design: Vol. 2. SAS. New York: Univer. Press of America.
BOCK,R. (1975) Multiuariate statistical methods in behavioral research. New York: McGraw-Hill. CRARY,M., FUCCI,D.,
&
BOND,Z. (1981) Interaction of sensory feedback: a child-adult com-
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parison of oral sensory and temporal articulatory function. Perceptual and Motor Skills, 53, 979-988.
Cunns, A. P, & FUCCI,D. (1983) Sensory and motor changes during development and aging. In N. Lass (Ed.), Speech atid language. Vol. 9. New York: Academic Press. Pp. 154-237. F u c c ~ ,D., HARRIS, D., & PETROSINO,L. (1984) Sensation magnitude scales for vibrotactile stimulation of the tongue and thenar eminence. Perceptual and Motor Skills, 58, 843-848.
F u c c ~ ,D., & PETROSMO,L. (1983) Lingual vibrotactile sensation magnitudes: comparison of suprathreshold responses for three different age ranges. Perceptual and Motor Skills, 57, 31-38.
F u c c ~ D., , P E ~ O S I N L., O , HARRIS,D., & RANDOLPH-TYLER, E. (1987) Effects of aging on responses to suprathreshold lingual vibrotactile stimulation. Perceptual and Motor Skills, 64, 683-694.
F u c c ~ ,D., PETROSINO, L.,HARRIS, D., RANDOLPH-TYLER, E., & WAGNER, S. (1989) Lingual vibmtactile threshold shift during magnitude-estimation scaling effects on magnitude-estimation responses and scaling behavior. Perception & Psychop srcs, 46, 275-278. F u c c ~ D., , PETROSINO, L., & ROBEY,R. (1982) Auditory m a s h g effects on lingual vibrotactile thresholds as a function of age. Perceptual and Motor Skills, 54, 945-950. F u c c ~ ,D., PETROSINO, L., SCHUSTER,S., & WAGNER,S. (1990) Comparison of lingual vibrotactile suprathreshold numerical responses in men and women: effects of threshold shift during magnitude-estimation scaling. Perceptual and Motor Skills, 70, 483-492. FUCCI, D., P E ~ O S I N O L.,, & WAGNER, S. (1989) Vibmtactile threshold shift during magnitude-estimation scaling on the hand: effects on magnitude-estimation responses and scaling behavior. Perceptual and Motor Skills, 69, 187-194. HALL,D., FUCCI,D., & ARNST,D. (1972) Vibrotactile stimulation: an investigation of psychophysical methods for establishing threshold. Perceptual and Motor Skills, 34, 891-898. HARPER, R., & STEVENS,S. S. (1964) Subjective hardness of compliant materials. Quarterly Journal ofExperimenta1 Psychology, 16, 204-215. HARRIS,D., FUCCI,D., PETROSINO, L., & WALLACE,L. (1986) Instrumentation for magnitude estimation and cross-modality matching of auditory and lingual vibrotactile sensations. Review of Scientific Insburnents, 57, 2343-2347. HELLMAN,R. P., & ZWISLOCKI,J. (1963) Monaural loudness function at 1000 cps and interaural summation. Journal ofthe Acoustical Society of America, 35, 856-865. HULL, R. (1978) Hearing evaluation of the elderly. In J. Katz (Ed.), Handbook of clinical audiology. Baltimore, MD: W i a m s & Willdns. Pp. 426-441. PETROSINO, L., & FUCCI,D. (1983) A precision method for lingual vibrotactile threshold measurement. Bulletin of the Psychonomic Society, 21, 203-205. PETROSINO, L., FUCCI,D., & HARRIS,D. (1785) Effects of single session repetitive judgments on magnitude estimation scales for lingual vibrotactile sensation. Perception & Psychopbysics, 37, 205-208. PETROSMO, L., FUCCI,D., & HARRIS,D. (1987) Magnitude estimation and magnitude production: stimulus frequency effects on magnitudes of lingual vibrotactile sensation. Perceptual and Motor Skills, 64, 663-670. PETROSINO, L., FUCCI,D., & ROBEY,R. (1982) Changes in lingual sensitivity as a function of age and stimulus exposure time. Perceptual and Motor Skills, 55, 1083-1090. STEVENS,S. S. (1955) The measurement of loudness. journal of the Acoustical Society of America, 27, 815-820. TELAGE,K., & FUCCI, D. (1974) Concerning intrasubject measurements of successive lingual vibrotactile responses. Perceptual and Motor Skills, 39, 1047-1052. VFXRULO,R. T. (1777) Comparisons of child and adult vibrotactile thresholds. Bulletin of the Psychonomic Society, 9, 197-200. VER~ILLO, R. T. (1980) Age-related changes in the sensitivity to vibration. Journal of Gerontology, 3 5 , 185-193. VERRILLO,R. T. (1982) Effects of aging on the suprathreshold responses to vibration. Perception & Psychophysics, 32, 61-68. VERRILLO,R. T., & CI-{AMBERLAIN, S. C. (1972) The effect of neural density and contactor surround on vibrotactile sensation magnitude. Perception & Prychophysics, 11, 117-120.
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VERRILLO,R. T.,FRAIOU,A. J., & SMITH, R. L. (1769) Sensation magnitude of vibrotactile stimuli. Perception C Psychopbysics, 6, 366-372.
WELFORD,A. T.(1780) Sensory, perceptual and motor processes in older adults. In J. E. Birren & R. B. Sloane (Eds.), Handbook of mental health and aging. Englewood Cliffs, NJ: Prentice-Hall. Pp. 172-213.
ZWSLOCKI,J. J., & GOODMAN, D. A. (1980) Absolute scaling of sensory magnitudes: a validation. Perception 6 Psychopbysics, 28, 28-38.
Accepted Junuary 28, 199 1
LINGUAL VIBROTACTILE THRESHOLD SHIFT DURING MAGNITUDE-ESTIMATION SCALING: EFFECTS O N MAGNITUDE-ESTIMATION RESPONSES AND SCALING BEHAVIOR ACROSS AGE ' DONALD FUCCI
LINDA PETROSINO
Ohio University, Athens, Ohio
Bowling Green Slate University Bowling Green, Ohio
SUSAN B. SCHUSTER AND ELIZABETH RANDOLPH Ohio Uniuersiiy, Athens, Ohio Summary.-The purpose of this study was to investigate the effects of age on tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Relationships of the Lingual vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were explored. Three groups differing in mean age participated in this study (Group 1 8.05 yr., Group 2 19.46 yr., and Group 3 56.2 yr.). Each subject performed two rnagnitude-estimation tasks. In one task, threshold of sensitivity was measured after every suprathreshold numerical response of the subject. If a threshold shift was recorded, threshold was allowed to return to the pretest baseline level continuing to the next suprathreshold stimulus presentation. The results showed that threshold shift during magnitude-estimation scaling took place for all three age groups and that the shiFt was related to the intensity of the suprathreshold vibratory stimulus being applied to the tongue. They also showed that Group 2 (young adults) performed magnitude-estimation scaling differently when threshold shift was controlled than when it was not. The other two groups of subjects were not similarly affected.
Psychophysical study of the tactile sensory system has been conducted at both threshold and suprathreshold levels through the use of vibratory
stimuli. Threshold investigation has provided information about the sensitivity of the receptor mechanism, and suprathreshold investigation has increased the understanding of the behavior of the tactile sense above the peripheral level of detectability. Recently a series of studies have been conducted which have addressed possible relationships between threshold and suprathreshold tactile function. These studies have looked at the effects of thIeshold shifts occurring during magnitude-estimation scaling (Fucci, Petrosino, Harris, Randolph-Tyler, & Wagner, 1989; Fucci, Petrosino, Schuster, & Wagner, 1990; Fucci, Petrosino, & Wagner, 1789). The effects of aging on thresholds of detection for the sense of touch have been studied in detail (Crary, Fucci, & Bond, 1781; Curtis & Fucci, 1983; Fucci, Petrosino, & Robey, 1982; Petrosino, Fucci, & Robey, 1782; 'Request reprints fmm Dr. Donald Fucci, School of Hearing and Speech Sciences, Ohio University, Athens, O H 45701.
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Verrillo, 1977, 1980). In general, research has shown that tactile thresholds derived from various body locations show a decrease in sensitivity with an increase in age. Aging effects with regard to suprathreshold tactile stimuli have also received some attention (Fucci & Petrosino, 1983; Fucci, Petrosino, Harris, & Randolph-Tyler, 1987; Verrillo, 1982). This research has shown that there is an aging effect for suprathreshold stimulus presentations to various body sites just as there is for tactile threshold of sensitivity. The purpose of the present experiment was to investigate three age groups with regard to tactile sensory system function by studying the effects of tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Relationships of these lingual vibrotactile threshold shifts to suprathreshold-stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were evaluated for each of the three age groups studied.
METHOD Subjects Three groups of subjects participated in this study. The first group, 12 girls and 8 boys, ranged in age from 6 to 9 years (M age = 8.05 yr.). The second group, 12 women and 12 men, ranged in age from 18 to 22 years (M age = 19.46 yr.). The third group, 10 women and 10 men, ranged in age from 50 to 69 years (M age = 56.2 yr.). All subjects had normal speech and hearing and were screened (by interview) for the presence of medical or physical conditions which could have interfered with test results. Apparatus The vibrotactile stimulus-control unit included a sine-wave generator, an experimenter-controlled variable attenuator, a riselfall gate, two universal timers, an audioamplifier, a power amplifier, and an electromagnetic rninivibrator with a probe-contactor extension. The pulsed vibratory signal generated had a frequency of 250 Hz, a 50% duty cycle (on 500 msec. and off 500 msec.) and a rise-fall time of 50 msec. The vibrotactile stimulusmeasurement unit included an accelerometer, a cathode follower, a rnicrophone amplifier, and a voltmeter. The auditory-masking unit consisted of a masking generator and TDH-49P headphones. The masking unit was used to present a narrow band of noise centered around 250 H z at 70 dB H T L bilaterally. A detailed description of the vibrotactile equipment and procedures can be found in a review by Harris, Fucci, Petrosino, and Wallace (1986). Procedure Each subject completed a series of two lingual vibrotactile magnitude-estimation scaling tasks, which were conducted in separate test sessions scheduled one week apart (Stevens, 1955). For both scaling tasks, the subject
AGE AND LINGUAL VIBROTACTILE THRESHOLD SHIFT
185
was seated in an adjustable chair and positioned so that the tongue could be placed against the bottom of a rigidly mounted plastic disk. A hole in the center of the disk provided access for the probe-contactor extension of the vibrator to the anterior midline section of the dorsum of the tongue. The contactor on the end of the probe had an area of ,128 cm2 and there was a 1-mm gap between the contactor and the disk. The TDH-49P headphones were placed over the subject's ears for binaural auditory masking of the 250-Hz vibrotactile stimulus being applied to the tongue. An ascending method of limits was used to obtain threshold of sensitivity for all subjects prior to each of the two magnitude-estimation tasks (Hall, Fucci, & Arnst, 1972). This method of threshold testing was chosen over the forced-choice criterion-free method of threshold testing to minimize subjects' fatigue and sensory-system adaptation (Petrosino & Fucci, 1983). Accepted threshold was the mean of three successive readings within a 5-mV range (Telage & Fucci, 1974). These obtained thresholds were necessary so the suprathreshold intensities for magnitude estimation could be set in reference to each subject's threshold of sensitivity (Verrillo, Fraioli, & Smith, 1969). They were also necessary in this experiment for determination of threshold shift and for the return of threshold to baseline in the second magnitude-estimation scaling task. During the first lingual vibrotactile magnitude-estimation task, each subject was required to assign numbers to a series of pulsed 250-Hz vibrotactile stimuli at eight randomly presented stimulus-intensity levels, ranging from 6 to 40 dB SL (6, 10, 16, 20, 26, 30, 36, and 40 dB SL). The subject was required to feel the pulsed, 250-Hz stimulus on the tongue for 15 sec. before being required to provide a numerical response. The subject was instructed to think of a number that matched the strength of the vibration felt on the tongue. Whole numbers, decimals, and fractions were indicated as permissible selections (Zwislocki & Goodman, 1980). The subjects were encouraged to be spontaneous in selecting numbers and to make judgments at each stimulus-intensity without reference to those previously presented. After each recording of the subject's verbal numerical response, the tongue was realigned with the probe-contactor extension of the vibrator in preparation for the subsequent stimulus presentation. For each group, the geometric means of the subjects' numerical responses to a single run of each of the eight stimulus intensities were taken as the mean lingual vibrotactile magnitude-estimation responses for that group. The variabhty of subject numerical responses was not calculated. Geometric means are designed to account for extreme score values in either direction from the mean. They are used for statistical summarization of magnitude-scahng data which will often show large differences in the actual numerical responses provided (Petrosino, Fucci, & Harris, 1985).
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During the second scaling task, lingual vibrotactile magnitude-estimation scaling was conducted in a manner similar to that described for the first sealing task, with two procedural changes. First, immediately after the subject provided a verbal numerical response to the 15-sec. presentation of the pulsed, 250-Hz stimulus at one of the eight intensities, lingual vibrotactile threshold of sensitivity was rechecked using the threshold technique described above. This postmagnitude-estimation response-threshold determination allowed the experimenter to assess threshold shift resulting from the suprathreshold-stimulus presentation. Second, if threshold shift was detected, the experimenter performed subsequent threshold checks until threshold returned to the prescaling baseline sensitivity level, before continuing to the next suprathreshold-stimulus presentation. In this manner, the experimenter was assured that each subsequent suprathreshold-stimulus presentation was initiated with the subject's threshold at the prescaling baseline. Postmagnitudeestimation response-threshold determinations were conducted for each of the eight randomly presented suprathreshold-stimulus presentations. Lingual vibrotactile threshold shifts for each subject at each of the eight suprathreshold-stimulus intensities were recorded in decibels sensation level and averaged for each group. The geometric means of each group's numerical responses to a single run of each of the eight stimulus-intensities were taken as the mean responses for the second scaling task (Petrosino, Fucci, & Harris, 1985). A counterbalanced technique was utilized to control for possible learning effects with regard to the lingual vibrotactile scaling tasks. Half of the subjects in each group performed the first scaling task during the first test session and the second scaling task during the second test session conducted one week later. The remaining subjects in each group performed the second scaling task during the first test session and the first scaling task during the second test session conducted one week later.
I t can be seen in Fig. 1 that threshold shift occurred for all three groups of subjects for each of the eight suprathreshold stimulus intensities employed in the magnitude-estimation scaling task on which a threshold check was conducted after each subject's numerical response. A two-factor, mixed design analysis of variance with repeated measures on one factor was performed on the threshold-shift data (Barcikowski, 1983; Bock, 1975). No significant differences among the groups were noted (p = .06). The children, young adults, and older individuals tested performed similarly with respect to threshold shift that occurred during magnitude-estimation scaling. The threshold-shift data for all groups combined, showed a strong relationship between the amount of threshold shift occurring and stimulus intensity
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( p < .001). Amount of threshold shift showed a consistent increase with an increase in stimulus intensity. An analysis of variance of three-factor, mixed design with repeated measures on two factors was performed on the magnitude-estimation scaling data (Barcikowski, 1983; Bock, 1975). Over-all differences were found among the three groups of subjects. The three groups performed differently on the scaling tasks with regard to the eight stimulus intensities for both test conditions (where threshold checks were not made and where threshold checks were made) ( p = .02). Post hoc testing using Paired Comparisons indicated that the group of subjects comprised of children (Group 1) performed differently on the scaling tasks with regard to the eight stimulus intensities for both test conditions than the group of subjects comprised of young adults (Group 2) and the group of subjects comprised of older individuals (Group 3). Groups 2 and 3 performed similarly on the scaling tasks for both test conditions. A linear trend analysis indicated that as intensity was increased, the numerical magnitude-estimation responses for atl three groups of subjects increased in a linear fashion (p = .03).
-
Threshold Shift -
0= 0=
Group 1(Age Range 6-9) Group 2 (Age Range 18-22) = Group 3 (Age Range 50-69)
I
I
I
I
I
Stimulus Intensity Levels (dB SL) FIG.1. Threshold shift on the tongue, for three age groups, as a function of suprathreshold stimulus intensity
All three groups of subjects combined did not perform the magnitudeestimation scaling tasks differently for the test condition where threshold checks were not made as opposed to the condition where threshold checks were made ( p = .12). A three-way interaction (p = .02, for groups, conditions, intensities) prompted further testing in which a two-factor mixed design with repeated measures on one factor was performed on each group separately
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(Barcikowski, 1783; Bock, 1775). A difference was found in the magnitude-estimation responses of the young adults for the two scaling conditions ( p = .006). Mean lower and upper power function exponents were derived for each group of subjects for the two scaling tasks employed in this experiment. The exponents are reported in terms of intensity (VerriUo & Chamberlain, 1972). It appears that lingual vibrotactile magnitude-estimation scales may show a limitation in magnitude growth functions around and above 25 dB SL. Harper and Stevens (1753) hypothesized that for certain continua, an "upper threshold" may exist and that above this region, increases in stimulus values show no corresponding gradations in subjective magnitude. The present magnitude-estimations for the three groups reflected such an asymptotic growth function and are consistent with previous research (Fucci, Harris, & Petrosino, 1784; Petrosino, Fucci, & Harris, 1785, 1787). The mean exponents for the lower functions for Group 1, were .58 for the scaling task on which no threshold checks were made, and .56 for the scaling task on which threshold checks were made. The mean exponents for the upper functions for Group 1, were .35 for the no-threshold-check condition, and .45 for the threshold-check condition. For Group 2, the mean exponents for the lower functions were .58 for the no-threshold-check condition, and .54 for the threshold-check condition. The mean exponents for the upper functions for Group 2 were .16 for the no-threshold-check condition and .21 for the threshold-check condition. For Group 3, the mean exponents for the lower functions were .62 for the no-threshold-check condition, and .52 for the threshold-check condition. The mean exponents for the upper slopes for Group 3 were .17 for the no-threshold-check condition, and .14 for the threshold-check condition. A one-factor multivariate analysis of variance performed on the power function data indicated that there were no significant differences among the three groups of subjects for the lower power functions for the two magnitude-estimation scaling conditions (p = .82; p = .78) (Barcikowski, 1983; Bock, 1775). There were significant differences among the three groups of subjects for the upper power functions for both scaling conditions (p = .005; p = .024). Post hoc testing using paired comparisons indicated that the Group 1 subjects provided upper power functions for both test conditions that were statistically different than those of the other two groups of subjects. The young adults and older individuals provided both lower and upper power functions that were statistically similar for both test conditions.
D~scussro~ The results of this study indicate that threshold shift can occur for different age groups during lingual vibrotactile magnitude-estimation scaling when a 250-Hz stimulus of 15 sec. duration is employed. They further show
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that the amount of threshold shift is directly related to the intensity of the suprathreshold stimulus. The threshold shifting that occurred in this study was statistically similar for the three different age groups employed (Fig. 1). The numerical responses of the young adult subjects (Group 2) to the suprathreshold stimulus intensities appear to have been influenced by the threshold shifts that occurred during the magnitude-estimation scaling tasks. The numerical responses of the children (Group 1) and the older individuals (Group 3) did not appear to be similarly influenced by threshold shifts. The young adult subjects consistently provided higher numerical responses at each of the eight suprathreshold intensities for the task in which threshold was allowed to return to prescaling baseline than they did for the task in which possible threshold shift was not determined or controlled during the scaling procedure. It is possible that the young adults were using threshold of sensitivity as a reference for their scaling behavior and that they used this reference differently when it was free to vary as opposed to when it was controlled and set at baseline levels for each suprathreshold stimulus presentation. A reference standard was deliberately not employed in the scaling procedure (Hellrnan & Zwislocki, 1963). Informal questioning of the young adult subjects after testing was completed indicated that most of them had been using an internal referent of their own during magnitude-estimation scaling. The most likely chosen referent was what the subjects thought to be the weakest vibratory sensation that they could feel on their tongues. When the cMdren were asked how they dealt with the scaling procedure they, as a group, were more prone to suggest that they just provided numbers that matched the intensities that they were feeling on their tongues. They did not seem to be using a reference of any kind during the magnitude-estimation scaling. It has been suggested that children, unlike adults, do not have fully formulated internal numerical references (Zwislocki & Goodman, 1980). The older group of individuals (Group 3), like the children, did not feel that the threshold concept was very important to the scahng process. The older group of individuals appeared to be more cautious during the entire testing procedure and wanted more external input from the experimenter as to whether they were performing the task appropriately. It is known that the natural aging process leads to a more "cautious" response behavior in formal testing situations (Aiken, 1980; Hull, 1978; Welford, 1980). The Group 3 subjects appeared to be looking for an external referent to be provided by the experimenter. The children, as a group, performed differently than the other two groups of subjects with regard to the magnitude-estimation scaling for both the no-threshold-check and the threshold-check conditions. More specifically, they provided different sets of numerical responses to the upper four stimulus intensities than the other two groups. This finding can be seen with
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regard to the mean upper power function exponents (reported above), which were much higher for the children than they were for the young adults and older individuals. The children, although their scaling responses showed some degree of asymptotic behavior, came closer to a scaling function that was a straight line throughout the entire range of the eight stimulus intensity levels employed. This kind of scaling behavior in children has been noted in previous studies (Fucci & Petrosino, 1983; Fucci, Petrosino, Harris, & Randolph-Tyler, 1987). It appears that children approach the scaling task differently. They show little caution and provide numbers that do not relate to a particular reference value whether it be threshold of sensitivity or some other numerical set. The results of this study suggest that during magnitude-estimation scaling, shifts in threshold of sensitivity take place that relate to the amount of intensity of the suprathreshold vibratory stimulus being applied to the tongue. This appears to be the case for groups representing different age ranges. These threshold shifts appeared to have an influence on magnitude-estimation scaling results for the group representing young adults, but did not appear to influence scaling results for the groups representing children and older individuals. These two groups of subjects did not seem to relate what was happening at the sensory detection level to the scaling tasks by showing less concern for the need to have an internal referent to relate their numerical responses to. The children appeared to find the magnitude-estimation tasks easy to perform and readily provided numbers anchored only to what they were feeling on their tongues. The older individuals showed a large degree of concern about the scaling tasks, but looked more toward external guidance than a steady internal referent they were using. Threshold shift is an activity that can occur during vibrotactile magnitude-estimation scaling, even when the stimulus involved is of minimal duration and intensity. Threshold shift should be a recognized activity that can influence the suprathreshold numerical responses subjects provide. The results of this particular study suggest that threshold shift has the greatest influence on suprathreshold scaling for individuals who would be classified as young adults. Researchers involved in magnitude-estimation scaling research should be aware of the possibility that threshold shift might influence suprathreshold scaling activities and that age is a possible factor as to the extent of that influence. REFERENCES
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Accepted Junuary 28, 199 1
