Neuropsy&hgia, Vol. 30, No. 4. pp. 393491, Printed in Great Britain.
C028-3932/92 15.00+0.00 Pergamon Press Ltd
1992.
PERCEPTION OF MOVING AND STATIONARY GRATINGS IN BRAIN DAMAGED PATIENTS WITH UNILATERAL SPATIAL NEGLECT D~NATELLASPINELLI*and PIERLUIGIZOCCOLOTTI Dipartimento di Psicologia, Universita di Roma “La Sapienza”, Roma, Italy (Received 13 July 1991; accepted 13 November 1991) Ahstract4ontrast sensitivity for stationary and drifting sinusoidal gratings of different spatial frequencies was measured in 17 brain damaged patients (five left-brain damaged and 12 right-brain damaged patients, six of whom showed symptoms of spatial hemi-neglect). Twenty-nine combinations of spatio-temporal stimuli were considered in the drifting condition. No specific deficit for the group of patients with neglect symptom in the perception of moving and stationary gratings was observed. Also, no systematic deficit for perceiving the direction of motion-toward the neglect hemispace or away from it-was apparent. A small, selective impairment in the detection of stationary or very slow drifting gratings of low spatial frequency was observed in the presence of unilateral cortical damage, independently from its side (left or right) and from the presence of neglect. Some difficulty to detect the direction of motion was observed in a few individual patients.
INTRODUCTION THE ROLEof
basic sensory processes in spatial neglect has been a matter of debate. Early theories stressed the influence of visual field defects and impaired visual scanning in the syndrome [2,5,6,8]. However, it appears that field defects per se do not produce neglect and that neglect can be found in visual processing tasks where it is unlikely that eye movements mediate performance (for a review see Ref. [3]). More recently, it has been proposed that early sensory processes may interact with later processes in producing the characteristic clinical picture of spatial neglect [ 131. The quality of basic sensory processing, in humans as well as in animals, can be assessed by the contrast sensitivity function. Contrast sensitivity has been measured in patients having symptoms of visual spatial neglect with conflicting results. KOBAYASHI et al. [ 121 showed an impairment of basic visual function specific for neglect patients. In contrast, SPINELLI et al. [19] observed a reduction in contrast sensitivity-restricted to the low frequency band-for right-brain damaged patients as compared to controls. However, this impairment was not specific for the patients with neglect. In the present work our previous observation was confirmed in a new group of neglect patients, and a small group of left-brain damaged patients was also included. Moreover, since to date only contrast sensitivity function for stationary objects has been considered, in *Address for correspondence: Donatella Spinelli, Dipartimento di Psicologia, Via dei Marsi 78, 00185 Roma, Italy. 393
394
D. SPINELLI and P. ZOCCOLO~TI
order to gain new information on the visual perception of patients with hem&neglect, measurements relative to moving objects vision were taken. There are relatively few data in the literature concerning vision of motion in brain damaged patients, and they are generally relative to patients with posterior (mostly bilateral) cortical lesions. Individual cases of patients suffering from a specific disorder of movement perception have been documented in neurological literature [17,22]; cases have also been reported showing selective deficits for temporal frequency [ 161 and exposure duration [9,11, 201; on the other hand, Hess et al. [lo] did not observe any selective impairment, but a general attenuation in contrast sensitivity for moving stimuli. Examining patients with right occipito-temporal or occipito-parietal lesions;V~~~~ [21] observed selective impairments in the interpretation of visual motion in different tasks (speed discrimination, structure from motion, form from motion). Contrast sensitivity for moving spatial frequency gratings has not yet been systematically investigated in patients with unilateral spatial neglect. A large range of different spatiotemporal conditions was tested in the present work. Moreover, since asymmetrical space exploration is a part of the neglect symptom, the presence of asymmetries for the direction of motion was also considered.
METHOD Subjects Seventeen brain damaged patients were examined. Five had a CVA confined to the left hemisphere, 12 to the right hemisphere (one of these with a small focus also in the left frontal hemisphere, patient No. 5 in Table 1). According to the standard procedures in use in the laboratory (see neuropsychological tests) signs of unilateral neglect were present in six (RBD-neglect) and absent in the remaining six (RBD) patients. Brain lesions were documented by CT scan or by NMR in 13 patients. Table 1 shows summary of the neurological, demographic and neuropsychological characteristics of the patients included in the study. A control group of five subjects without brain damage was tested for comparison. The control group was comparable to the patients group for age. Tests Neuropsychological battery. The battery used consisted of two cancellation tests, one reading test and the Wundt-Jastrow Area Illusion test [14]. Neglect patients failed in at least two of these tests, according to established cut-off scores [15]. RBD patients had normal performance throughout the test battery. Contrast sensitivity to stationary stimuli. Sinusoidal gratings of vertical orientation were electronically generated on to a TV screen (LACE Elettronica; 65 frames/set; phosphor V50-21OOM-W-7L). The mean luminance of the screen was 120 cd/m’. The viewing distance was 114 cm. The visual display subtended 15 degrees of visual angle. The spatial frequencies tested were: 0.25,0.5,1,2 and 5 c/deg. The contrast is defined as &,,,,,- L,,,/L,,, + L,i,. The contrast sensitivity is defined as the reciprocal of contrast threshold. The stimulus contrast varied continously at low values (from 0.1 to 2%) and by fixed steps of 6 db at high values (from 2 to 84%). The gratings were stationary. Contrast sensitivity to mouingstimuli. In this case the stimuli described above were made to drift on the screen. The direction of drift could be from left to right or vice versa. The speed of the motion varied. Speed of motion, i.e. velocity, of a visual display was expressed in deg/sec. At constant velocity, a low spatial frequency grating (i.e. large bars) appears to drift slower than a high frequency grating (narrow bars). Since in the experiment the spatial frequency of gratings varied, the notation of temporal frequency was used, according to the literature [l]. A grating drifting at a constant velocity (u) has a single spatial frequency (SF, measured in c/deg) and temporal frequency (TF, measured in cjsec): TF/SF=u. The following 29 combinations of spatio-temporal stimuli were considered: SF=0.25 c/deg, TF=0.125,0.25,0.5, 1, 1.87,6.25, 12.5 c/set; SF=0.5 c/deg, TF=0.25,0.5, 1,2, 3.75,6.25, 12.5, 25c/sec; SF=1 c/deg, TFc0.5, 1, 2, 3, 7.5, 12.5, 25, 5Oc/sec; SF=2c/deg,TF=1,2,4, 6, 8, lOc/sec. Note in Fig. 2 that the ranges of temporal frequencies explored with gratings of different spatial frequency only partly overlap: at 0.25 c/deg the lowest temporal frequencies were tested, at 1 and 2 c/deg the highest. For technical reasons it was not possible at 2 c/deg to test the sensitivity at temporal frequencies higher than 10 Hz. Direction ofmotion. A number oftrials (about 35%), randomly chosen, were added in 13 patients (5 RBD-neglect, 3 RBD, 5 LBD) to compare the contrast sensitivity to motion in either direction. The contrasts required to discriminate the direction of a sinusoidal grating drifting from right to left and from left
PERCEPTION
OF MOVING
AND
STATIONARY
GRATINGS
IN BRAIN
DAMAGED
PATIENTS
395
Table 1. Summary of the neurological, neuropsychological and demographic characteristics of the patients included in the study. Details of the site of lesions were included when NMR(or TC) were available. Otherwise right (R) localization was indicated, according to clinical evaluation. (P = parietal; T = temporal; 0 = occipital; F = frontal). ______===_=___*____I_=====____IL==_==_r_-*~=---======__- __=I== patients
symbol
sex
age
time from onset
lesions
neglect
1 2 3 4 5
F M M F F
66 I; 55 74
3 4 4 4 6
present present present present present
6
F
58
3 months
RFTP R 0 P RTP RFTP R 0 P+ LF R T P
7 6 9
M F M
64 65 71
3years 4years 3 months
absent absent absent
10 11 12
M M M
74 65 70
2.9 years 3 months 7 months
R R R int. capsu1a R R Rbasal ganglia and polls
months months years months months
13 * M 61 6 months L 0 T 14 0 M 5: 6 years LT n 15 F 7 months L FTP 16 . M 69 5 months L T P 17 0 M 70 2 years LFTP ~=~~PP~L~~I*.~~~~~~~==---Pl-----I----P~=~~~.~~~~~~~~~~~~~~~~~~~~~~~
present
absent absent absent
absent absent absent absent absent
to right were measured in each particular condition of grating size (spatial frequency) and speed (temporal frequency). The two contrast sensitivities were calculated, then, the ratio between the two was computed. Procedure The tests 2,3 and 4 were carried out in two-four sessions, depending on the cooperation of the patient. Test 1 was carried out on a separate session. For stationary contrast sensitivity measurements, the subjects were instructed through observation of all gratings at high contrast; the contrast of the gratings was reduced to 0.1% (below the threshold), then increased up to high contrast. The subjects task was to say when the grating was detectable. When the task was clearly understood, the thresholds were evaluated by the method of adjustment, with two successive measurements for each trial. To check the reliability of the patients, 10% of blank trials were randomly inserted. For the measurement of motion contrast sensitivity the subjects were instructed through observation of various gratings of high contrast drifting to the left and to the right at various speeds. The contrast of the grating was reduced to O.l%, then increased. The subjects tasks was to discriminate the direction of the grating. The direction of drift varied in a pseudo-random sequence. When the task was clear the thresholds were measured by the adjustment method, with two successive measurements for each condition. Data were collected for each spatial frequency, varying randomly the speed and the direction. Ten per cent of blank trials were inserted. In all conditions presentation time was essentially unlimited. Three LBD patients were aphasic and used the hand to indicate the direction. All the patients easily understood the task. One RBD subject (No. 9 in the table), discharged from hospital, was not submitted to test No. 2.
RESULTS
Contrast sensitivity for stationary stimuli Constrast sensitivity to stationary gratings for the three groups of patients is presented in Fig. 1. As expected, the spatial frequency had a clear effect on the contrast threshold
396
D.
and P.
SPINELLI
ZOCCOLO~TI
(F=30.36; 4, 68 d.f.; P
C028-3932/92 15.00+0.00 Pergamon Press Ltd
1992.
PERCEPTION OF MOVING AND STATIONARY GRATINGS IN BRAIN DAMAGED PATIENTS WITH UNILATERAL SPATIAL NEGLECT D~NATELLASPINELLI*and PIERLUIGIZOCCOLOTTI Dipartimento di Psicologia, Universita di Roma “La Sapienza”, Roma, Italy (Received 13 July 1991; accepted 13 November 1991) Ahstract4ontrast sensitivity for stationary and drifting sinusoidal gratings of different spatial frequencies was measured in 17 brain damaged patients (five left-brain damaged and 12 right-brain damaged patients, six of whom showed symptoms of spatial hemi-neglect). Twenty-nine combinations of spatio-temporal stimuli were considered in the drifting condition. No specific deficit for the group of patients with neglect symptom in the perception of moving and stationary gratings was observed. Also, no systematic deficit for perceiving the direction of motion-toward the neglect hemispace or away from it-was apparent. A small, selective impairment in the detection of stationary or very slow drifting gratings of low spatial frequency was observed in the presence of unilateral cortical damage, independently from its side (left or right) and from the presence of neglect. Some difficulty to detect the direction of motion was observed in a few individual patients.
INTRODUCTION THE ROLEof
basic sensory processes in spatial neglect has been a matter of debate. Early theories stressed the influence of visual field defects and impaired visual scanning in the syndrome [2,5,6,8]. However, it appears that field defects per se do not produce neglect and that neglect can be found in visual processing tasks where it is unlikely that eye movements mediate performance (for a review see Ref. [3]). More recently, it has been proposed that early sensory processes may interact with later processes in producing the characteristic clinical picture of spatial neglect [ 131. The quality of basic sensory processing, in humans as well as in animals, can be assessed by the contrast sensitivity function. Contrast sensitivity has been measured in patients having symptoms of visual spatial neglect with conflicting results. KOBAYASHI et al. [ 121 showed an impairment of basic visual function specific for neglect patients. In contrast, SPINELLI et al. [19] observed a reduction in contrast sensitivity-restricted to the low frequency band-for right-brain damaged patients as compared to controls. However, this impairment was not specific for the patients with neglect. In the present work our previous observation was confirmed in a new group of neglect patients, and a small group of left-brain damaged patients was also included. Moreover, since to date only contrast sensitivity function for stationary objects has been considered, in *Address for correspondence: Donatella Spinelli, Dipartimento di Psicologia, Via dei Marsi 78, 00185 Roma, Italy. 393
394
D. SPINELLI and P. ZOCCOLO~TI
order to gain new information on the visual perception of patients with hem&neglect, measurements relative to moving objects vision were taken. There are relatively few data in the literature concerning vision of motion in brain damaged patients, and they are generally relative to patients with posterior (mostly bilateral) cortical lesions. Individual cases of patients suffering from a specific disorder of movement perception have been documented in neurological literature [17,22]; cases have also been reported showing selective deficits for temporal frequency [ 161 and exposure duration [9,11, 201; on the other hand, Hess et al. [lo] did not observe any selective impairment, but a general attenuation in contrast sensitivity for moving stimuli. Examining patients with right occipito-temporal or occipito-parietal lesions;V~~~~ [21] observed selective impairments in the interpretation of visual motion in different tasks (speed discrimination, structure from motion, form from motion). Contrast sensitivity for moving spatial frequency gratings has not yet been systematically investigated in patients with unilateral spatial neglect. A large range of different spatiotemporal conditions was tested in the present work. Moreover, since asymmetrical space exploration is a part of the neglect symptom, the presence of asymmetries for the direction of motion was also considered.
METHOD Subjects Seventeen brain damaged patients were examined. Five had a CVA confined to the left hemisphere, 12 to the right hemisphere (one of these with a small focus also in the left frontal hemisphere, patient No. 5 in Table 1). According to the standard procedures in use in the laboratory (see neuropsychological tests) signs of unilateral neglect were present in six (RBD-neglect) and absent in the remaining six (RBD) patients. Brain lesions were documented by CT scan or by NMR in 13 patients. Table 1 shows summary of the neurological, demographic and neuropsychological characteristics of the patients included in the study. A control group of five subjects without brain damage was tested for comparison. The control group was comparable to the patients group for age. Tests Neuropsychological battery. The battery used consisted of two cancellation tests, one reading test and the Wundt-Jastrow Area Illusion test [14]. Neglect patients failed in at least two of these tests, according to established cut-off scores [15]. RBD patients had normal performance throughout the test battery. Contrast sensitivity to stationary stimuli. Sinusoidal gratings of vertical orientation were electronically generated on to a TV screen (LACE Elettronica; 65 frames/set; phosphor V50-21OOM-W-7L). The mean luminance of the screen was 120 cd/m’. The viewing distance was 114 cm. The visual display subtended 15 degrees of visual angle. The spatial frequencies tested were: 0.25,0.5,1,2 and 5 c/deg. The contrast is defined as &,,,,,- L,,,/L,,, + L,i,. The contrast sensitivity is defined as the reciprocal of contrast threshold. The stimulus contrast varied continously at low values (from 0.1 to 2%) and by fixed steps of 6 db at high values (from 2 to 84%). The gratings were stationary. Contrast sensitivity to mouingstimuli. In this case the stimuli described above were made to drift on the screen. The direction of drift could be from left to right or vice versa. The speed of the motion varied. Speed of motion, i.e. velocity, of a visual display was expressed in deg/sec. At constant velocity, a low spatial frequency grating (i.e. large bars) appears to drift slower than a high frequency grating (narrow bars). Since in the experiment the spatial frequency of gratings varied, the notation of temporal frequency was used, according to the literature [l]. A grating drifting at a constant velocity (u) has a single spatial frequency (SF, measured in c/deg) and temporal frequency (TF, measured in cjsec): TF/SF=u. The following 29 combinations of spatio-temporal stimuli were considered: SF=0.25 c/deg, TF=0.125,0.25,0.5, 1, 1.87,6.25, 12.5 c/set; SF=0.5 c/deg, TF=0.25,0.5, 1,2, 3.75,6.25, 12.5, 25c/sec; SF=1 c/deg, TFc0.5, 1, 2, 3, 7.5, 12.5, 25, 5Oc/sec; SF=2c/deg,TF=1,2,4, 6, 8, lOc/sec. Note in Fig. 2 that the ranges of temporal frequencies explored with gratings of different spatial frequency only partly overlap: at 0.25 c/deg the lowest temporal frequencies were tested, at 1 and 2 c/deg the highest. For technical reasons it was not possible at 2 c/deg to test the sensitivity at temporal frequencies higher than 10 Hz. Direction ofmotion. A number oftrials (about 35%), randomly chosen, were added in 13 patients (5 RBD-neglect, 3 RBD, 5 LBD) to compare the contrast sensitivity to motion in either direction. The contrasts required to discriminate the direction of a sinusoidal grating drifting from right to left and from left
PERCEPTION
OF MOVING
AND
STATIONARY
GRATINGS
IN BRAIN
DAMAGED
PATIENTS
395
Table 1. Summary of the neurological, neuropsychological and demographic characteristics of the patients included in the study. Details of the site of lesions were included when NMR(or TC) were available. Otherwise right (R) localization was indicated, according to clinical evaluation. (P = parietal; T = temporal; 0 = occipital; F = frontal). ______===_=___*____I_=====____IL==_==_r_-*~=---======__- __=I== patients
symbol
sex
age
time from onset
lesions
neglect
1 2 3 4 5
F M M F F
66 I; 55 74
3 4 4 4 6
present present present present present
6
F
58
3 months
RFTP R 0 P RTP RFTP R 0 P+ LF R T P
7 6 9
M F M
64 65 71
3years 4years 3 months
absent absent absent
10 11 12
M M M
74 65 70
2.9 years 3 months 7 months
R R R int. capsu1a R R Rbasal ganglia and polls
months months years months months
13 * M 61 6 months L 0 T 14 0 M 5: 6 years LT n 15 F 7 months L FTP 16 . M 69 5 months L T P 17 0 M 70 2 years LFTP ~=~~PP~L~~I*.~~~~~~~==---Pl-----I----P~=~~~.~~~~~~~~~~~~~~~~~~~~~~~
present
absent absent absent
absent absent absent absent absent
to right were measured in each particular condition of grating size (spatial frequency) and speed (temporal frequency). The two contrast sensitivities were calculated, then, the ratio between the two was computed. Procedure The tests 2,3 and 4 were carried out in two-four sessions, depending on the cooperation of the patient. Test 1 was carried out on a separate session. For stationary contrast sensitivity measurements, the subjects were instructed through observation of all gratings at high contrast; the contrast of the gratings was reduced to 0.1% (below the threshold), then increased up to high contrast. The subjects task was to say when the grating was detectable. When the task was clearly understood, the thresholds were evaluated by the method of adjustment, with two successive measurements for each trial. To check the reliability of the patients, 10% of blank trials were randomly inserted. For the measurement of motion contrast sensitivity the subjects were instructed through observation of various gratings of high contrast drifting to the left and to the right at various speeds. The contrast of the grating was reduced to O.l%, then increased. The subjects tasks was to discriminate the direction of the grating. The direction of drift varied in a pseudo-random sequence. When the task was clear the thresholds were measured by the adjustment method, with two successive measurements for each condition. Data were collected for each spatial frequency, varying randomly the speed and the direction. Ten per cent of blank trials were inserted. In all conditions presentation time was essentially unlimited. Three LBD patients were aphasic and used the hand to indicate the direction. All the patients easily understood the task. One RBD subject (No. 9 in the table), discharged from hospital, was not submitted to test No. 2.
RESULTS
Contrast sensitivity for stationary stimuli Constrast sensitivity to stationary gratings for the three groups of patients is presented in Fig. 1. As expected, the spatial frequency had a clear effect on the contrast threshold
396
D.
and P.
SPINELLI
ZOCCOLO~TI
(F=30.36; 4, 68 d.f.; P
