Neuropsychologia,1975,Vol. 13.pp. 213 to 218.Pergamon Press. Printedin England.
REACTION TIME TO HEMIRETINAL STIMULATION RALPH
Department
J. MADDESS
of Psychology, University of Victoria, Victoria, British Columbia, Canada (Received 23 July 1974)
Abstract-Reaction time to stimulation of the nasal hemiretinae was compared to stimulation of the temporal hemiretinae. The stimulus was a spot of light projected above and to the left or right of fixation. Subjects were divided into four groups according to eyedness and handedness. The major hypothesis was confirmed showing faster reaction time to stimulation of the crossed optic fibers than to stimulation of the uncrossed optic fibers (P < 0400001). Righteyed subjects were faster than left-eyed subjects (P < 0.05) but there was no difference between right and left handed subjects. Reaction time was faster with the dominant hand than with the non-dominant hand (P = 0400035). There were no significant interactions.
A CURRENT research technique of great importance in the study of brain-function relationships is the tachistoscopic paradigm. The tachistoscopic paradigm consists of the simultaneous or successive presentation of verbal or non-verbal material to a subject who is fixating a central point. The use of this paradigm in recognition and memory studies has resulted in controversial findings which have not, as yet, been adequately explained. WHITE [l] reviews tachistoscopic studies concerning one or more of the variables of cerebral dominance, selective retinal training, directional scanning, selective attention, stimulus structure, anisotrophy of visual space, ocular dominance, visual acuity, and immediate memory. It is of interest to determine, as well, if there are differences between the crossed (nasal) and uncrossed (temporal) optic tracts that could contribute variance to the experimental results. The importance of the optic tract variable has been indicated mainly in studies utilizing simultaneous exposure. Significantly better recall for digits projected to the nasal retinae has been found when digit pairs were presented one to each eye separately [2, 31 and during binocular fixation [4]. Nasal superiority has also been found in the reporting of a spaced string of digits [5], in color rivalry [S], and in the reproduction of complex stimulus patterns [6]. Monocular, non-competitive stimulation, on the other hand, has resulted in temporal superiority [7, 81. There is some physiological and anatomical evidence indicating that the crossed optic tract is superior to the uncrossed for both bilateral and unilateral stimulation. The crossed optic tracts dominate the uncrossed optic tracts during binocular rivalry [9] and there is a greater activation of cortical units in the crossed hemisphere of cats during unilateral stimulation [ 10-121. There is some indirect evidence that nervous transmission is also more rapid in the crossed pathways. Depth responses to stereolines presented at slightly different times indicate that nervous transmission is 1.5 msec faster in the crossed fibers [13]. Reaction time has been found to be faster following nasal than temporal stimulation [14, 151. Reaction time is relevant to both relative cortical unit activation and speed of nervous transmission since it is directly proportional to latency of evoked potentials and inversely proportional 213
214
RALPH J. MADDFS
to amplitude of evoked potentials [16]. The two reaction time studies were, however, considered to have provided only preliminary evidence due to a number of methodological defects. The purpose of this study was to replicate in part the HALL and KRIES [14] and POFFENRERGER[15] studies with improved apparatus, experimental design, and greater number of subjects. The primary hypothesis was that reaction time would be faster to stimulation of the nasal hemiretinae (crossed optic fibers) than to stimulation of the temporal hemiretinae (uncrossed optic fibers). METHOD Subjects
The subjects were 40 male university students with normal and equal eye acuity (20/20 -J=10). There wcrc 10 subjects in each of four groups which consisted of individuals who were either right handed-right eye dominant, right handed-left eye dominant, left handed-right eye dominant, or left handed-left eye dominant. Handedness was determined by an individually administered handedness questionnaire [17] and a finger aiming test [18], and by the A-B-C Test for Ocular Dominance [19]. Apparatus
The experiment was conducted in a flat black “perception tunnel”. The illumination level was adjustable and maintained at 6.00 log ppL. Two independent Kodak carousel 35 mm projectors with 500 watt bulbs were used for stimulus presentation. The projectors were adjusted so that the projection field of each completely coincided with the other (48.26 x 78.74 cm). The distance from the projectors to the screen was 1.83 m. Stimulus slides were presented with one projector, while the other projector was used to present a symmetrical cross fixation marker in the center of the screen and to maintain a constant illumination level. Each bar of the cross was 4 cm long by 1 cm wide (0.94’ x 0.24” visual angle). The stimuli were projected by a Kodak carouse1 750 projector through a special shutter which is controlled by a Gerbrands “300” Series Digital Millisecond Timer. This device allows for stimulus durations as short as 5 milliseconds (& 0.005 per cent). The projectors were placed on top of a 152 cm high, 122 cm X 122 cm metal enclosure. Foam rubber was placed under the projectors to mask vibrations. A standard telegraph key was directly in front of the subject on a desk attached to the front of the stationary enclosure. The subject sat within the enclosure, with his head held stable by means of a Haag/Strat chin-rest and forehead brace mounted on the desk. This arrangement allowed for the projectors to be the same distance to the screen as were the subject’s eyes and yet be completely hidden from view. A dual tape programmer was used to initiate a 0.75 set warning tone and a digital timer which controlled the tachistoscope shutters. No two subjects received the same treatment series. The warning tone was presented to the subject through Telex SC-20 Stereo-twin headphones by an EICO-Model377 Audio Generator. The tone, a 40 dB sine wave (50 Hz) interrupted the otherwise continuous white noise (40 dB) used to mask the shutter sounds. The white noise (40 dB) was produced by a Marietta (style NA-36) White Noise Generator. Both the tone and white noise were amplified by an EICO (HFIZA) amplifier. The tone and white noise intensities were measured with a Scott 200 Sound Level Meter, pressed against the inside of the earphone. There were 80 presentation slides with 76 stimulus slides and 4 slides which informed the subject which hand-eye combination he was to use for the next series of slides. The stimulus slides consisted of 3 mm dia holes punched in black film. The stimuli appeared on the screen as bright spots of light (7.00 logpl.tL) 17 cm to the right or left of fixation (4’ of visual angle). All stimuli were projected 39 cm above 6xation. The stimuli were all of the same size and appeared in the same position to the right or left of fixation. The stimuli were presented on a stationary flat black screen affixed to a vertical wood panel. Fixation was monitored by a technique which has been shown to be superior to the “sideview technique” and as accurate as the method involving identification of a fixation stimulus [20]. A monocular lens was mounted behind a hole in the screen. The subject was required to fixate a small spot of reflected light on the center of the lens face. By viewing the subject through the lens, the experimenter was able to observe accurately movements of the subject’s pupil, changes in hand or eye position, and eye blinking. The actuation of the stimulus shutter initiated a Hunter Klockounter (Model 120A, series D). Full depression of the telegraph key stopped the Klockounter. Procedure
The subject was first given an eye test (Snellen E Letter Chart; Imperial Optical Limited, Number 2). Subjects who did not have normal and equal-eye acuity (20/20 + 10) were rejected. Then the subject was
REACTION
TIME TO HEMIRETINAL
STIMULATION
215
given the A-B-C Test for Ocular Dominance f19] followed by the finger aiming test 1181.If the results of these two tests were consistent, the subject was considered acceptable regardless of the “degree” of dominance indicated by the ratio of the Miles Test. No subjects were rejected because of inconsistent eyedness responses. To determine handedness, the subject was given the hand preference questionnaire [17] and a finger tapping test of manual dexterity. The dexterity task consisted of having the subject press a key attached to a mechanical counter as many times as possible with the index finger during a ten second interval. Each hand was tested twice. If the results of these two tests were consistent, the subject was considered acceptable regardless of the “degree” of handedness ascertained fromeither measure. Two subjects were rejected because of inconsistent preference and dexterity responses. Each of these rejected subjects preferred his left hand but was, in fact, more dextrous on the finger tapping test with his right. The subject’s head was adjusted to a standard chin-rest so that the corner of each eye was level with a white dot on the sides of the forehead brace and, consequently, at the same level as the center of fixation. Prior to the experiment, the subject was read the instructions for the task and given a series of 36 practice trials. There were 4 slides consisting of the hand or eye directions mentioned previously. The subject was asked to fixate carefully on a small spot of stationary light in the center of the cross as soon as he heard the warning tone. The spot of light was a reflection of light shone through the fixation cross on to the lens face behind it. The subject was further instructed to depress the key completely and as rapidly as possible when the stimulus light appeared while maintaining constant fixation. To further impress the need for constant fixation upon the subject, he was told that the experimenter would be behind the screen carefully monitoring fixation through a telescope and recording his reaction times. If the subject was not fixated or if he blinked during a stimulus exposure that trial was rejected. The stimulus exposure was 100 msec for all subjects and for all presentations. This duration is less than the time necessary to make lateral eye movements (125-235 msec [21,22]), and yet was long enough to allow the subject to understand the direction slides. There were four stimulus situations. The stimulus was projected to the right visual field for half the trials and to the left visual field for the other half. The subject used his right hand-left eye (uncrossed optic tract) and right hand-right eye (crossed optic tract) during right visual field stimulation. He used his left handright eye (uncrossed optic tract) and left hand-left eye (crossed optic tract) during left visual field stimulation. This was done so that the hemisphere of stimulation was the main hemisphere controlling the reacting hand. This would, then, be the hemisphere contralateral to that hand. The particular order of conditions for each of the 40 subjects was chosen at random from a list of the 20 possible treatment orders.
ANALYSIS
AND
RESULTS
The original reaction time scores were analyzed by a 2 x 2 between groups (right/left eye dominant; right/left hand dominant) by a 2 x 2 within groups (crossed/uncrossed optic fibers; dominant/non-dominant hand analysis of variance. There were 9 repeated measures under each condition but the median score was extracted for analysis so that each subject had only one score per condition. Table 1 shows the reaction time means for the between main effects of hand and eye dominance and the within main effects of retinal stimulation and reaction hand. As shown in Table 1, all mean reaction times for main effects were in the low to mid-400 msec. Right hand dominant subjects were 20 msec faster than left hand dominant subjects (N.S.) and right eye dominant subjects were 39 msec faster than left eye dominant subjects Table 1. Reaction time means in msec: main effects Main effects Right hand dominant Left hand dominant
Means 415.750 434.075
Right eye dominant Left eye dominant
405.600 444.255
Contralateral stimulation lpsilateral stimulation
412.563 437.263
Dominant hand reaction Non-dominant hand reaction
418.638 431.188
216
RALPHJ.
MADDESS
(F = 5.899; & = 1; P < 0.05). Reaction time was faster to nasal stimulation than to temporal stimulation by 25 msec (F = 59.772; df = 1; P < O*OOOOOl;while the dominant hand was faster than the non-dominant hand by about 13 msec (F = 22.218; df = 1; P = OWOO36). Although the difference in mean reaction time is larger for the between subjects effects, the within effects are shown to be of greater importance due to the smaller treatment error variance. There were no significant interactions. DISCUSSION The results of this study support the major hypothesis that reaction time to stimulation of the crossed optic tracts is faster than reaction time to stimulation of the uncrossed optic tracts. This result reaffirms previous studies of reaction time to optic stimulation [14, 151. The highly significant difference was probably due to using a greater number of subjects and improved apparatus and design. Reaction time was significantly faster when subjects were reacting with their dominant vs their non-dominant hand. This was as expected on the basis of the imposed conformity between the hand preference questionnaire and the finger tapping dexterity task. The two within factors of crossed/uncrossed optic fibers and dominant hand/nondominant hand did not interact but rather combined to show the order of crossed x dominant hand < crossed x non-dominant hand < uncrossed x dominant hand < uncrossed x non-dominant hand where (
REACTION TIME TO HEMIRETINAL STIMULATION RALPH
Department
J. MADDESS
of Psychology, University of Victoria, Victoria, British Columbia, Canada (Received 23 July 1974)
Abstract-Reaction time to stimulation of the nasal hemiretinae was compared to stimulation of the temporal hemiretinae. The stimulus was a spot of light projected above and to the left or right of fixation. Subjects were divided into four groups according to eyedness and handedness. The major hypothesis was confirmed showing faster reaction time to stimulation of the crossed optic fibers than to stimulation of the uncrossed optic fibers (P < 0400001). Righteyed subjects were faster than left-eyed subjects (P < 0.05) but there was no difference between right and left handed subjects. Reaction time was faster with the dominant hand than with the non-dominant hand (P = 0400035). There were no significant interactions.
A CURRENT research technique of great importance in the study of brain-function relationships is the tachistoscopic paradigm. The tachistoscopic paradigm consists of the simultaneous or successive presentation of verbal or non-verbal material to a subject who is fixating a central point. The use of this paradigm in recognition and memory studies has resulted in controversial findings which have not, as yet, been adequately explained. WHITE [l] reviews tachistoscopic studies concerning one or more of the variables of cerebral dominance, selective retinal training, directional scanning, selective attention, stimulus structure, anisotrophy of visual space, ocular dominance, visual acuity, and immediate memory. It is of interest to determine, as well, if there are differences between the crossed (nasal) and uncrossed (temporal) optic tracts that could contribute variance to the experimental results. The importance of the optic tract variable has been indicated mainly in studies utilizing simultaneous exposure. Significantly better recall for digits projected to the nasal retinae has been found when digit pairs were presented one to each eye separately [2, 31 and during binocular fixation [4]. Nasal superiority has also been found in the reporting of a spaced string of digits [5], in color rivalry [S], and in the reproduction of complex stimulus patterns [6]. Monocular, non-competitive stimulation, on the other hand, has resulted in temporal superiority [7, 81. There is some physiological and anatomical evidence indicating that the crossed optic tract is superior to the uncrossed for both bilateral and unilateral stimulation. The crossed optic tracts dominate the uncrossed optic tracts during binocular rivalry [9] and there is a greater activation of cortical units in the crossed hemisphere of cats during unilateral stimulation [ 10-121. There is some indirect evidence that nervous transmission is also more rapid in the crossed pathways. Depth responses to stereolines presented at slightly different times indicate that nervous transmission is 1.5 msec faster in the crossed fibers [13]. Reaction time has been found to be faster following nasal than temporal stimulation [14, 151. Reaction time is relevant to both relative cortical unit activation and speed of nervous transmission since it is directly proportional to latency of evoked potentials and inversely proportional 213
214
RALPH J. MADDFS
to amplitude of evoked potentials [16]. The two reaction time studies were, however, considered to have provided only preliminary evidence due to a number of methodological defects. The purpose of this study was to replicate in part the HALL and KRIES [14] and POFFENRERGER[15] studies with improved apparatus, experimental design, and greater number of subjects. The primary hypothesis was that reaction time would be faster to stimulation of the nasal hemiretinae (crossed optic fibers) than to stimulation of the temporal hemiretinae (uncrossed optic fibers). METHOD Subjects
The subjects were 40 male university students with normal and equal eye acuity (20/20 -J=10). There wcrc 10 subjects in each of four groups which consisted of individuals who were either right handed-right eye dominant, right handed-left eye dominant, left handed-right eye dominant, or left handed-left eye dominant. Handedness was determined by an individually administered handedness questionnaire [17] and a finger aiming test [18], and by the A-B-C Test for Ocular Dominance [19]. Apparatus
The experiment was conducted in a flat black “perception tunnel”. The illumination level was adjustable and maintained at 6.00 log ppL. Two independent Kodak carousel 35 mm projectors with 500 watt bulbs were used for stimulus presentation. The projectors were adjusted so that the projection field of each completely coincided with the other (48.26 x 78.74 cm). The distance from the projectors to the screen was 1.83 m. Stimulus slides were presented with one projector, while the other projector was used to present a symmetrical cross fixation marker in the center of the screen and to maintain a constant illumination level. Each bar of the cross was 4 cm long by 1 cm wide (0.94’ x 0.24” visual angle). The stimuli were projected by a Kodak carouse1 750 projector through a special shutter which is controlled by a Gerbrands “300” Series Digital Millisecond Timer. This device allows for stimulus durations as short as 5 milliseconds (& 0.005 per cent). The projectors were placed on top of a 152 cm high, 122 cm X 122 cm metal enclosure. Foam rubber was placed under the projectors to mask vibrations. A standard telegraph key was directly in front of the subject on a desk attached to the front of the stationary enclosure. The subject sat within the enclosure, with his head held stable by means of a Haag/Strat chin-rest and forehead brace mounted on the desk. This arrangement allowed for the projectors to be the same distance to the screen as were the subject’s eyes and yet be completely hidden from view. A dual tape programmer was used to initiate a 0.75 set warning tone and a digital timer which controlled the tachistoscope shutters. No two subjects received the same treatment series. The warning tone was presented to the subject through Telex SC-20 Stereo-twin headphones by an EICO-Model377 Audio Generator. The tone, a 40 dB sine wave (50 Hz) interrupted the otherwise continuous white noise (40 dB) used to mask the shutter sounds. The white noise (40 dB) was produced by a Marietta (style NA-36) White Noise Generator. Both the tone and white noise were amplified by an EICO (HFIZA) amplifier. The tone and white noise intensities were measured with a Scott 200 Sound Level Meter, pressed against the inside of the earphone. There were 80 presentation slides with 76 stimulus slides and 4 slides which informed the subject which hand-eye combination he was to use for the next series of slides. The stimulus slides consisted of 3 mm dia holes punched in black film. The stimuli appeared on the screen as bright spots of light (7.00 logpl.tL) 17 cm to the right or left of fixation (4’ of visual angle). All stimuli were projected 39 cm above 6xation. The stimuli were all of the same size and appeared in the same position to the right or left of fixation. The stimuli were presented on a stationary flat black screen affixed to a vertical wood panel. Fixation was monitored by a technique which has been shown to be superior to the “sideview technique” and as accurate as the method involving identification of a fixation stimulus [20]. A monocular lens was mounted behind a hole in the screen. The subject was required to fixate a small spot of reflected light on the center of the lens face. By viewing the subject through the lens, the experimenter was able to observe accurately movements of the subject’s pupil, changes in hand or eye position, and eye blinking. The actuation of the stimulus shutter initiated a Hunter Klockounter (Model 120A, series D). Full depression of the telegraph key stopped the Klockounter. Procedure
The subject was first given an eye test (Snellen E Letter Chart; Imperial Optical Limited, Number 2). Subjects who did not have normal and equal-eye acuity (20/20 + 10) were rejected. Then the subject was
REACTION
TIME TO HEMIRETINAL
STIMULATION
215
given the A-B-C Test for Ocular Dominance f19] followed by the finger aiming test 1181.If the results of these two tests were consistent, the subject was considered acceptable regardless of the “degree” of dominance indicated by the ratio of the Miles Test. No subjects were rejected because of inconsistent eyedness responses. To determine handedness, the subject was given the hand preference questionnaire [17] and a finger tapping test of manual dexterity. The dexterity task consisted of having the subject press a key attached to a mechanical counter as many times as possible with the index finger during a ten second interval. Each hand was tested twice. If the results of these two tests were consistent, the subject was considered acceptable regardless of the “degree” of handedness ascertained fromeither measure. Two subjects were rejected because of inconsistent preference and dexterity responses. Each of these rejected subjects preferred his left hand but was, in fact, more dextrous on the finger tapping test with his right. The subject’s head was adjusted to a standard chin-rest so that the corner of each eye was level with a white dot on the sides of the forehead brace and, consequently, at the same level as the center of fixation. Prior to the experiment, the subject was read the instructions for the task and given a series of 36 practice trials. There were 4 slides consisting of the hand or eye directions mentioned previously. The subject was asked to fixate carefully on a small spot of stationary light in the center of the cross as soon as he heard the warning tone. The spot of light was a reflection of light shone through the fixation cross on to the lens face behind it. The subject was further instructed to depress the key completely and as rapidly as possible when the stimulus light appeared while maintaining constant fixation. To further impress the need for constant fixation upon the subject, he was told that the experimenter would be behind the screen carefully monitoring fixation through a telescope and recording his reaction times. If the subject was not fixated or if he blinked during a stimulus exposure that trial was rejected. The stimulus exposure was 100 msec for all subjects and for all presentations. This duration is less than the time necessary to make lateral eye movements (125-235 msec [21,22]), and yet was long enough to allow the subject to understand the direction slides. There were four stimulus situations. The stimulus was projected to the right visual field for half the trials and to the left visual field for the other half. The subject used his right hand-left eye (uncrossed optic tract) and right hand-right eye (crossed optic tract) during right visual field stimulation. He used his left handright eye (uncrossed optic tract) and left hand-left eye (crossed optic tract) during left visual field stimulation. This was done so that the hemisphere of stimulation was the main hemisphere controlling the reacting hand. This would, then, be the hemisphere contralateral to that hand. The particular order of conditions for each of the 40 subjects was chosen at random from a list of the 20 possible treatment orders.
ANALYSIS
AND
RESULTS
The original reaction time scores were analyzed by a 2 x 2 between groups (right/left eye dominant; right/left hand dominant) by a 2 x 2 within groups (crossed/uncrossed optic fibers; dominant/non-dominant hand analysis of variance. There were 9 repeated measures under each condition but the median score was extracted for analysis so that each subject had only one score per condition. Table 1 shows the reaction time means for the between main effects of hand and eye dominance and the within main effects of retinal stimulation and reaction hand. As shown in Table 1, all mean reaction times for main effects were in the low to mid-400 msec. Right hand dominant subjects were 20 msec faster than left hand dominant subjects (N.S.) and right eye dominant subjects were 39 msec faster than left eye dominant subjects Table 1. Reaction time means in msec: main effects Main effects Right hand dominant Left hand dominant
Means 415.750 434.075
Right eye dominant Left eye dominant
405.600 444.255
Contralateral stimulation lpsilateral stimulation
412.563 437.263
Dominant hand reaction Non-dominant hand reaction
418.638 431.188
216
RALPHJ.
MADDESS
(F = 5.899; & = 1; P < 0.05). Reaction time was faster to nasal stimulation than to temporal stimulation by 25 msec (F = 59.772; df = 1; P < O*OOOOOl;while the dominant hand was faster than the non-dominant hand by about 13 msec (F = 22.218; df = 1; P = OWOO36). Although the difference in mean reaction time is larger for the between subjects effects, the within effects are shown to be of greater importance due to the smaller treatment error variance. There were no significant interactions. DISCUSSION The results of this study support the major hypothesis that reaction time to stimulation of the crossed optic tracts is faster than reaction time to stimulation of the uncrossed optic tracts. This result reaffirms previous studies of reaction time to optic stimulation [14, 151. The highly significant difference was probably due to using a greater number of subjects and improved apparatus and design. Reaction time was significantly faster when subjects were reacting with their dominant vs their non-dominant hand. This was as expected on the basis of the imposed conformity between the hand preference questionnaire and the finger tapping dexterity task. The two within factors of crossed/uncrossed optic fibers and dominant hand/nondominant hand did not interact but rather combined to show the order of crossed x dominant hand < crossed x non-dominant hand < uncrossed x dominant hand < uncrossed x non-dominant hand where (
