SIMPLE REACTION TIME TO LATERALIZED VISUAL STIMULI IS NOT RELATED TO THE HEMISPHERIC SIDE OF LESION G.P. Anzola and L.A. Vignolo (Clinica Neurologica dell'Universita, Brescia, Italy)
It is generally agreed that brain-damaged patients have longer response latencies to brief visual or acoustic stimulation in comparison to healthy people matched for age and educational level (Benton, 1985; Milner, 1986). What is still matter of debate is whether or not the side of the lesion is crucial for the lengthening of the reaction time (RT). Earlier data from Blackburn and Benton (1955) and Benton and Joynt (1959) showed that right brain-damaged (RBD) patients were as impaired as left brain-damaged (LBD) patients in RTs to visual stimuli. By contrast, in a comparable RT task, De Renzi and Faglioni (1965) found that RBD patients were slower than LBD patients. Further evidence was subsequently published by Howes and Boller (1975) in favor of the right hemisphere dominance for RTs, studying patients subjected to scintiscan. On the contrary, Tartaglione, Bino, Manzino et aI. (1986) failed to find a difference in RBD as compared to LBD patients in a consecutive series with CT scan verification of the lesions. A number of factors have been found to affect RTs: lesion size, lesion progression rate, associated neuropsychological abnormalities (De Renzi and Faglioni, 1965; Howes and Boller, 1975, Tartaglione, Oneto, Manzino et aI., 1987; Elsass and Hartelius, 1985; Kaizer, Korner-Bitensky, Mayo et aI., 1988). In all likelihood, the main reason for the discrepancy between the data of the literature is the poor control of these variables. Progression of the lesion, for instance, has been found to adversely affect RTs. In a study in which patients with stabilized vascular lesions were compared to patients with progressive neoplastic lesions matched for size, the latter were found more severely impaired (Elsass and Hartelius, 1985). By contrast, in a recent report, a sample presenting a mixture of vascular and neoplastic lesions, asymmetrically distributed in the brain, failed to show any interhemispheric difference (Tartaglione et aI., 1986). The modality of stimulation may be another important factor. In a recent paper (Kaizer et aI., 1988) visual stimuli were randomly flashed to either the right or left visual field in patients with unilateral cerebrovascular lesions. Despite the fact that the mean response latencies did not differ in RBD as compared to LBD patients, RBD patients were slower than LBD patients when stimuli appeared in the visual field contralateral to the brain lesion. These findings suggest that manipulating the stimulus presentation can uncover more subtle differences produced by right and left hemispheric lesions. Cortex, (1992) 28, 401-409
G.P. Anzola and L.A. Vignolo
402
In the present paper we have tried to reduce all the confounding variables to a minimum by selecting a homogeneous sample of patients with a single vascular lesion, as assessed by the patient's history and the CT scan, and free of severe neuropsychological abnormalities. In addition, we have chosen an experimental design in which the visual stimuli were delivered to either visual field, either randomly or in blocked sequences. The aim of the study was twofold: first, to assess whether the side of the lesion is crucial for the overall lengthening of RTs; second, to investigate whether the hemifield in which the stimulus is presented is relevant for RTs impairment. MATERIALS AND METHODS
Patients One-hundred twenty three consecutive patients were considered as candidates for this study since 1988; of these, however, only 39 were included, due to the strict criteria that we have adopted, namely: - Age between 20 and 75 years. - Full right-handedness at the Edinburgh Handedness Inventory (Oldfield, 1971). - Neurological examination and/or CT scan data pointing to one single brain lesion, localized in either hemisphere. - No history of previous brain damage, including T.I.A.s. - No present or past evidence of drug or alcohol addiction. - Cerebrovascular etiology (either infarct or hemorrhage). - Time elapsed from stroke between 1 day and 6 weeks. - Patients physically able to undergo the testing sessions. - No current therapy with barbiturates or tranquillizers. - Absence of severe neuropsychological deficits that could impair attention or task comprehension. There were 20 right brain-damaged (RBD) and 19 left brain-damaged (LBD) patients. Their characteristics are shown in Table I. Due to the inclusion criteria, all RBD patients with clinically overt hemineglect and all LBD patients with the severest forms of global or Wernicke's aphasia were excluded. Two left brain-damaged patients had moderate Broca's aphasia. Neuropsychological Tests Reaction Times Simple visual reaction times (RTs) were assessed by having the patients sitting in front of the screen of an Apple lIe, on which stimuli appeared with constant luminosity. The patient's position with respect to the screen was kept constant with the aid of a head-and-chinTABLE I
Characteristics of Patients
RBD LBD
N
M/F
Age (years)
Years of schooling
Post stroke (days)
CH
VFD
20 19
13/6
1515
50 56
5.9 6.6
18.5 22.0
2.5 2.9
0 0
RBD = right brain-damaged; LBD = left brain-damaged; N = number of patients; M/F= male/female; CH = contralateral hemiparesis (0 = no movement; I = possible spontaneously; 2 = possible against resistance; 3 = possible against gravity; 4 = normal); VFD = visual field defect. The figures for age, years of schooling, post·stroke days and CH are the means of the sample, those for M/F and VFD are the number of patients.
Reaction time in unilateral brain lesions
403
rest device, and he/she was asked to look at the fixation point, consisting of a small cross in the middle of the screen. The experimenter monitored the eye movements during the whole testing session. A brief acoustic signal preceded the appearance of the visual stimulus, which consisted of a bright spot. Two types of stimulus presentation were used, namely blocked (i.e., the spot appeared in the same location) and random (i.e. the spot appeared randomly in one of four possible locations). In the blocked presentations the spot could appear 3 degrees either to the right or to the left of the fixation point. Fifty consecutive presentations constituted one block. In the random presentations the stimulus could appear 3 degrees to the right, left, above or below the fixation point. There were no blank trials. Following the acoustic warning signal the spot appeared within a random interval of 100800 msec. and it lasted for 100 msec. The patient was asked to respond always with the hand ipsilateral to the cerebral lesion. The hand rested near the keyboard and the patient kept his/ her index finger on the appropriate key, which was the lower left or lower right one of the keyboard for the left and right hands, respectively. The patient was instructed to press the key as soon as he/she noticed the appearance of the spot. The RT had to fall between the ensuing 150 and 1500 msec. in order to be computed. Each patient underwent four experimental sessions (two blocked RTs and two random RTs sessions), which were given in random sequence. In the blocked RTs sessions the order of stimulation was balanced across and within patients. There was an interval of at least four hours between one session and the next, in order to minimize the effects of fatigue and learning. The RTs sessions took place on the average 20 days after the stroke (range 6-40). In each session the stimulus was presented 100 times in the right and 100 times in the left visual field, so that at the end of the experiment 200 RTs were collected in each condition (blocked or random) for each visual field (right or left). This means that blocked sessions included 200 trials and random sessions 400 trials. The performance of each patient was expressed by 4 median values of the RTs: two for the blocked stimulus condition (ipsi and contralateral visual field with respect to the cerebral lesion) and 2 for the random stimulus condition (ipsi and contralateral visual field).
Other Neuropsychological Tests (1) The Token Test (De Renzi and Vignolo, 1962, in the revised version of De Renzi and Faglioni, 1978), sensitive to lesions of the left hemisphere; (2) Benton's Line Orientation test (Benton, 1983), sensitive to lesions of the right hemisphere; (3) Raven Colored PM 1947 (see norms in Basso, Capitani and Laiacona, 1987), sensitive to brain damage in general.
Lesion Assessment The Locus of the lesion was identified by the CT scan and the cortical site was determined by reporting the lesion on a lateral outline of the hemisphere by means of a computerized version of the procedure described by Mazzocchi and Vignolo (1978). The volume of the lesion was assessed as follows: the area of the lesion was measured on each CT section by means of a high definition planimeter (Planix-Tamaya Digital). The partial volume of the lesion on each section was obtained by multiplying each area by the corresponding section width, taking into account the scale ratio of the film to the physical size (this value was available on the scout-view). The total volume of the lesion was obtained by summing up each partial volume. The first CT scan was performed from 0 to 40 days (mean = 13.75) following the stroke. The scans performed within the first two days were subsequently repeated on the seventh days post stroke. Only the scans performed beyond the second day were considered for lesion assessment.
404
G.P. Anzola and L.A. Vignolo TABLE II
a: Mean and SD (in parentheses) of Reaction Times in milliseconds Blocked stimulus
Right BD Left BD
Random stimulus
Ipsi
Contra
Ipsi
288 (92) 287 (94)
303 (l05) 302 (86)
305 (126) 294 (87)
Contra 329 (135)
318 (97)
b: Results of ANOVA on RTs (in milliseconds) Presentation Overall
Type
Side
Right BD 306 Left BD 300
Blocked 295 Random 311
Ipsilateral 293 Contralateral 313
n .s.
p
It is generally agreed that brain-damaged patients have longer response latencies to brief visual or acoustic stimulation in comparison to healthy people matched for age and educational level (Benton, 1985; Milner, 1986). What is still matter of debate is whether or not the side of the lesion is crucial for the lengthening of the reaction time (RT). Earlier data from Blackburn and Benton (1955) and Benton and Joynt (1959) showed that right brain-damaged (RBD) patients were as impaired as left brain-damaged (LBD) patients in RTs to visual stimuli. By contrast, in a comparable RT task, De Renzi and Faglioni (1965) found that RBD patients were slower than LBD patients. Further evidence was subsequently published by Howes and Boller (1975) in favor of the right hemisphere dominance for RTs, studying patients subjected to scintiscan. On the contrary, Tartaglione, Bino, Manzino et aI. (1986) failed to find a difference in RBD as compared to LBD patients in a consecutive series with CT scan verification of the lesions. A number of factors have been found to affect RTs: lesion size, lesion progression rate, associated neuropsychological abnormalities (De Renzi and Faglioni, 1965; Howes and Boller, 1975, Tartaglione, Oneto, Manzino et aI., 1987; Elsass and Hartelius, 1985; Kaizer, Korner-Bitensky, Mayo et aI., 1988). In all likelihood, the main reason for the discrepancy between the data of the literature is the poor control of these variables. Progression of the lesion, for instance, has been found to adversely affect RTs. In a study in which patients with stabilized vascular lesions were compared to patients with progressive neoplastic lesions matched for size, the latter were found more severely impaired (Elsass and Hartelius, 1985). By contrast, in a recent report, a sample presenting a mixture of vascular and neoplastic lesions, asymmetrically distributed in the brain, failed to show any interhemispheric difference (Tartaglione et aI., 1986). The modality of stimulation may be another important factor. In a recent paper (Kaizer et aI., 1988) visual stimuli were randomly flashed to either the right or left visual field in patients with unilateral cerebrovascular lesions. Despite the fact that the mean response latencies did not differ in RBD as compared to LBD patients, RBD patients were slower than LBD patients when stimuli appeared in the visual field contralateral to the brain lesion. These findings suggest that manipulating the stimulus presentation can uncover more subtle differences produced by right and left hemispheric lesions. Cortex, (1992) 28, 401-409
G.P. Anzola and L.A. Vignolo
402
In the present paper we have tried to reduce all the confounding variables to a minimum by selecting a homogeneous sample of patients with a single vascular lesion, as assessed by the patient's history and the CT scan, and free of severe neuropsychological abnormalities. In addition, we have chosen an experimental design in which the visual stimuli were delivered to either visual field, either randomly or in blocked sequences. The aim of the study was twofold: first, to assess whether the side of the lesion is crucial for the overall lengthening of RTs; second, to investigate whether the hemifield in which the stimulus is presented is relevant for RTs impairment. MATERIALS AND METHODS
Patients One-hundred twenty three consecutive patients were considered as candidates for this study since 1988; of these, however, only 39 were included, due to the strict criteria that we have adopted, namely: - Age between 20 and 75 years. - Full right-handedness at the Edinburgh Handedness Inventory (Oldfield, 1971). - Neurological examination and/or CT scan data pointing to one single brain lesion, localized in either hemisphere. - No history of previous brain damage, including T.I.A.s. - No present or past evidence of drug or alcohol addiction. - Cerebrovascular etiology (either infarct or hemorrhage). - Time elapsed from stroke between 1 day and 6 weeks. - Patients physically able to undergo the testing sessions. - No current therapy with barbiturates or tranquillizers. - Absence of severe neuropsychological deficits that could impair attention or task comprehension. There were 20 right brain-damaged (RBD) and 19 left brain-damaged (LBD) patients. Their characteristics are shown in Table I. Due to the inclusion criteria, all RBD patients with clinically overt hemineglect and all LBD patients with the severest forms of global or Wernicke's aphasia were excluded. Two left brain-damaged patients had moderate Broca's aphasia. Neuropsychological Tests Reaction Times Simple visual reaction times (RTs) were assessed by having the patients sitting in front of the screen of an Apple lIe, on which stimuli appeared with constant luminosity. The patient's position with respect to the screen was kept constant with the aid of a head-and-chinTABLE I
Characteristics of Patients
RBD LBD
N
M/F
Age (years)
Years of schooling
Post stroke (days)
CH
VFD
20 19
13/6
1515
50 56
5.9 6.6
18.5 22.0
2.5 2.9
0 0
RBD = right brain-damaged; LBD = left brain-damaged; N = number of patients; M/F= male/female; CH = contralateral hemiparesis (0 = no movement; I = possible spontaneously; 2 = possible against resistance; 3 = possible against gravity; 4 = normal); VFD = visual field defect. The figures for age, years of schooling, post·stroke days and CH are the means of the sample, those for M/F and VFD are the number of patients.
Reaction time in unilateral brain lesions
403
rest device, and he/she was asked to look at the fixation point, consisting of a small cross in the middle of the screen. The experimenter monitored the eye movements during the whole testing session. A brief acoustic signal preceded the appearance of the visual stimulus, which consisted of a bright spot. Two types of stimulus presentation were used, namely blocked (i.e., the spot appeared in the same location) and random (i.e. the spot appeared randomly in one of four possible locations). In the blocked presentations the spot could appear 3 degrees either to the right or to the left of the fixation point. Fifty consecutive presentations constituted one block. In the random presentations the stimulus could appear 3 degrees to the right, left, above or below the fixation point. There were no blank trials. Following the acoustic warning signal the spot appeared within a random interval of 100800 msec. and it lasted for 100 msec. The patient was asked to respond always with the hand ipsilateral to the cerebral lesion. The hand rested near the keyboard and the patient kept his/ her index finger on the appropriate key, which was the lower left or lower right one of the keyboard for the left and right hands, respectively. The patient was instructed to press the key as soon as he/she noticed the appearance of the spot. The RT had to fall between the ensuing 150 and 1500 msec. in order to be computed. Each patient underwent four experimental sessions (two blocked RTs and two random RTs sessions), which were given in random sequence. In the blocked RTs sessions the order of stimulation was balanced across and within patients. There was an interval of at least four hours between one session and the next, in order to minimize the effects of fatigue and learning. The RTs sessions took place on the average 20 days after the stroke (range 6-40). In each session the stimulus was presented 100 times in the right and 100 times in the left visual field, so that at the end of the experiment 200 RTs were collected in each condition (blocked or random) for each visual field (right or left). This means that blocked sessions included 200 trials and random sessions 400 trials. The performance of each patient was expressed by 4 median values of the RTs: two for the blocked stimulus condition (ipsi and contralateral visual field with respect to the cerebral lesion) and 2 for the random stimulus condition (ipsi and contralateral visual field).
Other Neuropsychological Tests (1) The Token Test (De Renzi and Vignolo, 1962, in the revised version of De Renzi and Faglioni, 1978), sensitive to lesions of the left hemisphere; (2) Benton's Line Orientation test (Benton, 1983), sensitive to lesions of the right hemisphere; (3) Raven Colored PM 1947 (see norms in Basso, Capitani and Laiacona, 1987), sensitive to brain damage in general.
Lesion Assessment The Locus of the lesion was identified by the CT scan and the cortical site was determined by reporting the lesion on a lateral outline of the hemisphere by means of a computerized version of the procedure described by Mazzocchi and Vignolo (1978). The volume of the lesion was assessed as follows: the area of the lesion was measured on each CT section by means of a high definition planimeter (Planix-Tamaya Digital). The partial volume of the lesion on each section was obtained by multiplying each area by the corresponding section width, taking into account the scale ratio of the film to the physical size (this value was available on the scout-view). The total volume of the lesion was obtained by summing up each partial volume. The first CT scan was performed from 0 to 40 days (mean = 13.75) following the stroke. The scans performed within the first two days were subsequently repeated on the seventh days post stroke. Only the scans performed beyond the second day were considered for lesion assessment.
404
G.P. Anzola and L.A. Vignolo TABLE II
a: Mean and SD (in parentheses) of Reaction Times in milliseconds Blocked stimulus
Right BD Left BD
Random stimulus
Ipsi
Contra
Ipsi
288 (92) 287 (94)
303 (l05) 302 (86)
305 (126) 294 (87)
Contra 329 (135)
318 (97)
b: Results of ANOVA on RTs (in milliseconds) Presentation Overall
Type
Side
Right BD 306 Left BD 300
Blocked 295 Random 311
Ipsilateral 293 Contralateral 313
n .s.
p
