Psychological Research
Psychol. Res. 40, 5 3 - 6 4 (1978)
© by Springer-Verlag • 1978
Perception of Weight and Volume of Functional Objects as Judged by the Sighted and Blind T.M. Nelson, C.J. Ladan*, and J. Epps Department of Psychology, University of Alberta, Edmonton, Alberta T6G, Canada
,Summary. The manner in which sighted, sighted-but-blindfolded, late-blind (subsequent to 7 years of age), and congenitally blind (blind since birth) persons employ physical parameters in determining weight and volume of functional objects was studied. Eight stimuli each having a unique combination of physical specifications were judged, using both a match and estimate procedure. The results indicated that information derived from mass, displacement, and density provides the basis for volumetric and weight judgements of sighted persons. Nonsighted individuals employ this information differently than do sighted persons. Likewise, individuals after 7 years of age retain information provided by early visual experience and thus may employ a combination of kinesthetic and visual cues. The results also show that sighted and late-blind groups may employ visual perception or memory in determining volume, whereas sighted-but-blindfolded persons and the congenitally blind may employ mass in volumetric tasks. All groups may employ mass (and perhaps density) in determining weight, and although the weight judgements of non-sighted groups correlate highly with mass, sighted subjects are more accurate in judgement (i.e. have the smaller constant error). Sighted subjects apparently employ a complex system in determining weight. Age at which blindness occurred and the number of years of blindness had no effect for the late-blind group. Introduction
The thesis that vision is a primary perceptual experience is called into question by the work of Hebb (1949), Von Senden (1960), Gregory (1966), and Ackroyd, Humphrey and Warrington (1974) all of whom report that the congenitally blind upon regaining their sight are not initially able to deal with visual stimuli, but require a period during which the visual system adapts, or learning to perceive visually occurs. Further, it is accepted that differences in judgement and in variability of judgement occur between groups having different degrees of visual experience (Cutsforth, 1933; Revesz, 1950; *Now of the Family Studies Division, University of Alberta 0340-0727/78/0040/0053/$02.40
54
T.M. Nelson et al.
Von Senden, 1960; Bartley, 1967). For the small number of persons who are totally blind, visual experience may be expressed in terms of the age at which sight was lost, the number of years since the onset of blindness, and the nature of the causes leading to blindness. With respect to the etiology of blindness, the contribution of vision is understood through comparisons of the judgements of sighted with groups of persons who lack vision for various reasons. The degree of visual experience affects the performance and competence of the blind in complex and diverse ways. Nelson and Haney (1968) investigated the perception of early blind, late-blind, and sighted-but-blindfolded subjects and found judgements of force differed between sighted and other groups. Irrespective of the cause of blindness or the age at which blindness occurred, blind participants over-estimated the impact of objects which struck them, as compared to sighted groups. However, Nelson and MacDonald (1973) found the perception of cause-and-effect arising from tactilekinesthetic stimulation to be very similar in groups of early blind, late-blind, sighted, and sighted-but-blindfolded adults, i.e., sight proved unimportant in reported causal relations. Regarding aesthetic preference, the results are also discrepant. Hintz and Nelson (1971) found differences between blind groups in aesthetic appreciation of raised rectangular forms (haptic stimuli) and suggested that visual imagery may structure differences between judgements of the early blind as contrasted to late-blind, sighted-but-blindfolded, and sighted persons. Although comparisons of volume and weight judgements by blind and sighted groups have not been made, anomalies between perceived weight and perceived size (volume) have been documented for normally sighted groups. The most popular explanation (attributed to Thouless, 1931) suggests perceived density to be the basis for perception of the size-weight relationship (Ryan, 1940; Helson, 1964; Bartley, 1972). Other investigators, following the earlier endeavors of Scripture (1897), have formulated an equation for weight and size judgements specifying proportional relationships between these physical parameters. Alternatively, some researchers (Friedlander, 1920; Usnadze, 1931) suggest volume and weight judgements are derived exclusively from the visual perception of size. All the above hypotheses indirectly question the possibility of perception of volume by the congenitally blind. Each in its own Way predicts that spatial concepts cannot be accurately derived from tactile and/or kinesthetic contact isolated from vision. There are exceptions to the general rule, Huang (1945) has described a "sense of density", although at least one investigator (Anderson, 1970) has reported data questioning the density hypothesis. The present study is intended to determine whether the physical parameters of mass, displacement, and density, either singly or in combination, are employed in judgements of weight and volume I in common perceptual situations. Ordinary objects were explored by either the tactile or tactile-kinesthetic systems and judged for volume and weight by groups of congenitally blind (CB), late-blind (LB), sighted-but-blindfolded, i.e., blindfolded normals (BN), and normal sighted (N). 1In order to avoid a confusion of terms, the authors employ "weight" and "volume" to indicate judgement or response data. The physical parameters of mass, displacement and density a r e employed as a) the reference standard (the Point of Objective Equality) in calculation of the Constant Error and b) in correlation with the response data.
Perception of Functional Objects
55
Method
Participants Four groups of twelve subjects each served. Sighted or "normal" (N) and sighted-butblindfolded "normals" (BN) were matched in age, education, and general occupational levels to late-blind (LB) and congenitally blind (CB) adults. Blind participants recognized no impairment other than visual and were self-sufficient housewives, or were employed, as was more common, in telephone service industries. All non-sighted participants were individually contacted through personal connections of one author who has family contact with blind individuals. The congenitally blind were carefully screened, and only those persons with visual defects at birth and no residual vision past the age of 4 were selected. Through questioning we found that all who served understood Archimedes principle. The late-blind were also carefully selected to assure that they were of normal vision at, or after, 7 years of age. Age of blindness is specified because several studies (cited by Lowenfeld, 1963) show that individuals who lost sight prior to 7 years of age do not retain the ability to conceptualize spatial properties such as area. Groups were matched in age, t y p e of occupation, and sex. Observers ranged in age from 19 to 76, and the median of each group was 52 years of age. All late-blind observers lost their sight at 7 years of age or later; the typical (mean) number of years of blindness was 30.2.
Apparatus Eight (8) common objects were used as stimuli. The material composition and the physical properties of mass, displacement, and density are given for each object in Table 1. It may be noted that the common objects selected do not describe a single continuum on any of these properties, and thus they are unlike stimuli commonly employed in scaling studies. The current study does not attempt scaling, and instead selected objects that might occur in ordinary perceptual situations. The remainder of the apparatus consisted of two one-quart containers, water, and a graduated beaker.
Table 1. Physical characteristics of the eight common articles serving as stimulus objects Object
Material
Sphere Knob Dowel Propeller Hook Electrical junction box Smooth building block Unfinished casting
Rubber Composition Light wood Alloy Alloy Zinc-coated steel Wood
Mass (g)
Displacement (cm 3)
Densil~ (g/cm ~)
14.18 28.35 42.53 155.92 170.10
201.60 85.39 28.52 28.52
0.07 0.28 0.50 5.47 5.96
255.15
28.52
8.95
25EL15
227.66
1.12
2325.70
170.78
13.62
99.65
Lead
56
T.M. Nelson et al.
Procedure Prior to judgements trials, participants explored the opaque response containers and were encouraged to conceptualize their characteristics when empty and as they were gradually filled with water. Stimulus objects were also freely explored prior to experimentation. Subjects were encouraged to associate the objects with things, surfaces, functions, and shapes with which they were familiar. The experiment was designed to present all stimulus objects "free" and "fixed". In the "free" condition, they were offered by hand to the participant, who explored the stimulus with both hands, including the use of arm muscles. This is termed the "tactilekinesthetic" method. In the other set of trials, "fixed" objects were used. They were fixed to a shaft clamped in a vise, permitting only tactile exploration. Hence, this is termed the "tactile only" method. Objects Were presented according to two randomly-determined sequences, one for the "tactile only" method, the other for the "tactile-kinesthetic" method. Half the observers performed the tactile task first, while the other half began with the tactilekinesthetic task. Exploration time was not limited in either condition. For volumetric judgements, the subject was instructed "to attend to the size and shape of the object and judge how muchwater the object would hold if it were hollowed out to make an object with the thinnest walls imaginable or, alternatively, to judge how much water would run out of a pan filled to the brim if the object alone were very carefully slipped into it". The participant then matched the displacement by transferring water from one container to another (matching judgement). The participant could repeat pourings until he/she was satisfied with the judgements, and, in the case of overshoot, the trial was repeated. During matching participants inserted a hand or finger into the container receiving the water, in this way employing a method of depth estimation they commonly used in daily life. The experimenter measured the response by decanting the matched amount into the graduated beaker. Verbal estimations of displacement always preceded the matching condition and were given in terms of the number of tablespoons, cups, or pints of water judged to equal the object' s displacement. Participants choose and named the unit employed for each judgement. A series of standard questions testing each person's knowledge of measuring units and equivalents was given prior to experimentation to assure an equal knowledge of the use of these measures across groups. All participants demonstrated at least 90% accuracy in this task, with females proving more adept in use of the smaller units (teaspoons, tablespoons) than the male sample. Following completion of the volume measures, the same procedure was applied to weight judgements trials, but with the appropriate alterations in instructions. Here, as in volumetric trials, the stimulus object was always available for comparison during judgement. The participant was instructed to first provide verbal estimates of weight in fluid ounces and second, to decant a mass of water equal to the weight of the stimulus object. This was done by transferring water into the second container until the mass of water, by lift, appeared to match that of the stimulus object. The observer had previously explored and lifted the empty container, to familiarize himself with its weight so that this might be extracted from his total mass judgement of jar plus water.
Perception of Functional Objects
57
Results 2
The data were initially transformed to response error (the over-estimation or underestimation of the judgement as compared to the physical entity, in either displacement or mass units, dependent upon whether the judgement was volume or weight, respectively). An analysis of variance applied to the measures of volume showed reliable differences among groups, F (3, 44) = 3.48~ P < 0.05, response method, F (1, 44) = 4.09, P
Psychol. Res. 40, 5 3 - 6 4 (1978)
© by Springer-Verlag • 1978
Perception of Weight and Volume of Functional Objects as Judged by the Sighted and Blind T.M. Nelson, C.J. Ladan*, and J. Epps Department of Psychology, University of Alberta, Edmonton, Alberta T6G, Canada
,Summary. The manner in which sighted, sighted-but-blindfolded, late-blind (subsequent to 7 years of age), and congenitally blind (blind since birth) persons employ physical parameters in determining weight and volume of functional objects was studied. Eight stimuli each having a unique combination of physical specifications were judged, using both a match and estimate procedure. The results indicated that information derived from mass, displacement, and density provides the basis for volumetric and weight judgements of sighted persons. Nonsighted individuals employ this information differently than do sighted persons. Likewise, individuals after 7 years of age retain information provided by early visual experience and thus may employ a combination of kinesthetic and visual cues. The results also show that sighted and late-blind groups may employ visual perception or memory in determining volume, whereas sighted-but-blindfolded persons and the congenitally blind may employ mass in volumetric tasks. All groups may employ mass (and perhaps density) in determining weight, and although the weight judgements of non-sighted groups correlate highly with mass, sighted subjects are more accurate in judgement (i.e. have the smaller constant error). Sighted subjects apparently employ a complex system in determining weight. Age at which blindness occurred and the number of years of blindness had no effect for the late-blind group. Introduction
The thesis that vision is a primary perceptual experience is called into question by the work of Hebb (1949), Von Senden (1960), Gregory (1966), and Ackroyd, Humphrey and Warrington (1974) all of whom report that the congenitally blind upon regaining their sight are not initially able to deal with visual stimuli, but require a period during which the visual system adapts, or learning to perceive visually occurs. Further, it is accepted that differences in judgement and in variability of judgement occur between groups having different degrees of visual experience (Cutsforth, 1933; Revesz, 1950; *Now of the Family Studies Division, University of Alberta 0340-0727/78/0040/0053/$02.40
54
T.M. Nelson et al.
Von Senden, 1960; Bartley, 1967). For the small number of persons who are totally blind, visual experience may be expressed in terms of the age at which sight was lost, the number of years since the onset of blindness, and the nature of the causes leading to blindness. With respect to the etiology of blindness, the contribution of vision is understood through comparisons of the judgements of sighted with groups of persons who lack vision for various reasons. The degree of visual experience affects the performance and competence of the blind in complex and diverse ways. Nelson and Haney (1968) investigated the perception of early blind, late-blind, and sighted-but-blindfolded subjects and found judgements of force differed between sighted and other groups. Irrespective of the cause of blindness or the age at which blindness occurred, blind participants over-estimated the impact of objects which struck them, as compared to sighted groups. However, Nelson and MacDonald (1973) found the perception of cause-and-effect arising from tactilekinesthetic stimulation to be very similar in groups of early blind, late-blind, sighted, and sighted-but-blindfolded adults, i.e., sight proved unimportant in reported causal relations. Regarding aesthetic preference, the results are also discrepant. Hintz and Nelson (1971) found differences between blind groups in aesthetic appreciation of raised rectangular forms (haptic stimuli) and suggested that visual imagery may structure differences between judgements of the early blind as contrasted to late-blind, sighted-but-blindfolded, and sighted persons. Although comparisons of volume and weight judgements by blind and sighted groups have not been made, anomalies between perceived weight and perceived size (volume) have been documented for normally sighted groups. The most popular explanation (attributed to Thouless, 1931) suggests perceived density to be the basis for perception of the size-weight relationship (Ryan, 1940; Helson, 1964; Bartley, 1972). Other investigators, following the earlier endeavors of Scripture (1897), have formulated an equation for weight and size judgements specifying proportional relationships between these physical parameters. Alternatively, some researchers (Friedlander, 1920; Usnadze, 1931) suggest volume and weight judgements are derived exclusively from the visual perception of size. All the above hypotheses indirectly question the possibility of perception of volume by the congenitally blind. Each in its own Way predicts that spatial concepts cannot be accurately derived from tactile and/or kinesthetic contact isolated from vision. There are exceptions to the general rule, Huang (1945) has described a "sense of density", although at least one investigator (Anderson, 1970) has reported data questioning the density hypothesis. The present study is intended to determine whether the physical parameters of mass, displacement, and density, either singly or in combination, are employed in judgements of weight and volume I in common perceptual situations. Ordinary objects were explored by either the tactile or tactile-kinesthetic systems and judged for volume and weight by groups of congenitally blind (CB), late-blind (LB), sighted-but-blindfolded, i.e., blindfolded normals (BN), and normal sighted (N). 1In order to avoid a confusion of terms, the authors employ "weight" and "volume" to indicate judgement or response data. The physical parameters of mass, displacement and density a r e employed as a) the reference standard (the Point of Objective Equality) in calculation of the Constant Error and b) in correlation with the response data.
Perception of Functional Objects
55
Method
Participants Four groups of twelve subjects each served. Sighted or "normal" (N) and sighted-butblindfolded "normals" (BN) were matched in age, education, and general occupational levels to late-blind (LB) and congenitally blind (CB) adults. Blind participants recognized no impairment other than visual and were self-sufficient housewives, or were employed, as was more common, in telephone service industries. All non-sighted participants were individually contacted through personal connections of one author who has family contact with blind individuals. The congenitally blind were carefully screened, and only those persons with visual defects at birth and no residual vision past the age of 4 were selected. Through questioning we found that all who served understood Archimedes principle. The late-blind were also carefully selected to assure that they were of normal vision at, or after, 7 years of age. Age of blindness is specified because several studies (cited by Lowenfeld, 1963) show that individuals who lost sight prior to 7 years of age do not retain the ability to conceptualize spatial properties such as area. Groups were matched in age, t y p e of occupation, and sex. Observers ranged in age from 19 to 76, and the median of each group was 52 years of age. All late-blind observers lost their sight at 7 years of age or later; the typical (mean) number of years of blindness was 30.2.
Apparatus Eight (8) common objects were used as stimuli. The material composition and the physical properties of mass, displacement, and density are given for each object in Table 1. It may be noted that the common objects selected do not describe a single continuum on any of these properties, and thus they are unlike stimuli commonly employed in scaling studies. The current study does not attempt scaling, and instead selected objects that might occur in ordinary perceptual situations. The remainder of the apparatus consisted of two one-quart containers, water, and a graduated beaker.
Table 1. Physical characteristics of the eight common articles serving as stimulus objects Object
Material
Sphere Knob Dowel Propeller Hook Electrical junction box Smooth building block Unfinished casting
Rubber Composition Light wood Alloy Alloy Zinc-coated steel Wood
Mass (g)
Displacement (cm 3)
Densil~ (g/cm ~)
14.18 28.35 42.53 155.92 170.10
201.60 85.39 28.52 28.52
0.07 0.28 0.50 5.47 5.96
255.15
28.52
8.95
25EL15
227.66
1.12
2325.70
170.78
13.62
99.65
Lead
56
T.M. Nelson et al.
Procedure Prior to judgements trials, participants explored the opaque response containers and were encouraged to conceptualize their characteristics when empty and as they were gradually filled with water. Stimulus objects were also freely explored prior to experimentation. Subjects were encouraged to associate the objects with things, surfaces, functions, and shapes with which they were familiar. The experiment was designed to present all stimulus objects "free" and "fixed". In the "free" condition, they were offered by hand to the participant, who explored the stimulus with both hands, including the use of arm muscles. This is termed the "tactilekinesthetic" method. In the other set of trials, "fixed" objects were used. They were fixed to a shaft clamped in a vise, permitting only tactile exploration. Hence, this is termed the "tactile only" method. Objects Were presented according to two randomly-determined sequences, one for the "tactile only" method, the other for the "tactile-kinesthetic" method. Half the observers performed the tactile task first, while the other half began with the tactilekinesthetic task. Exploration time was not limited in either condition. For volumetric judgements, the subject was instructed "to attend to the size and shape of the object and judge how muchwater the object would hold if it were hollowed out to make an object with the thinnest walls imaginable or, alternatively, to judge how much water would run out of a pan filled to the brim if the object alone were very carefully slipped into it". The participant then matched the displacement by transferring water from one container to another (matching judgement). The participant could repeat pourings until he/she was satisfied with the judgements, and, in the case of overshoot, the trial was repeated. During matching participants inserted a hand or finger into the container receiving the water, in this way employing a method of depth estimation they commonly used in daily life. The experimenter measured the response by decanting the matched amount into the graduated beaker. Verbal estimations of displacement always preceded the matching condition and were given in terms of the number of tablespoons, cups, or pints of water judged to equal the object' s displacement. Participants choose and named the unit employed for each judgement. A series of standard questions testing each person's knowledge of measuring units and equivalents was given prior to experimentation to assure an equal knowledge of the use of these measures across groups. All participants demonstrated at least 90% accuracy in this task, with females proving more adept in use of the smaller units (teaspoons, tablespoons) than the male sample. Following completion of the volume measures, the same procedure was applied to weight judgements trials, but with the appropriate alterations in instructions. Here, as in volumetric trials, the stimulus object was always available for comparison during judgement. The participant was instructed to first provide verbal estimates of weight in fluid ounces and second, to decant a mass of water equal to the weight of the stimulus object. This was done by transferring water into the second container until the mass of water, by lift, appeared to match that of the stimulus object. The observer had previously explored and lifted the empty container, to familiarize himself with its weight so that this might be extracted from his total mass judgement of jar plus water.
Perception of Functional Objects
57
Results 2
The data were initially transformed to response error (the over-estimation or underestimation of the judgement as compared to the physical entity, in either displacement or mass units, dependent upon whether the judgement was volume or weight, respectively). An analysis of variance applied to the measures of volume showed reliable differences among groups, F (3, 44) = 3.48~ P < 0.05, response method, F (1, 44) = 4.09, P
