Roger W. Sperry’s research while affiliated with California Institute of Technology and other places

Six commissurotomized patients were tested and the performances of their left and right hemisphere on a dot counting task were compared during unilateral and bilateral input to study aspects of interhemispheric interference. From 1 to 5 dots were flashed, either in the left or the right visual field alone, or in each of the two fields simultaneously, and the patients were asked to indicate the number of dots seen in each field by extending the same number of fingers with the ipsilateral hand. Comparison trials were also presented where the number of dots were replaced by a corresponding numeral to eliminate counting. Comparable incidences of responses extinction to the dots and to the numerals were frequently observed during bilateral input. Their occurrence bore no clear relationship to the performance levels during unilateral input. Rather, the predominant side of extinction varied among the patients and seems to be related to the presence of some contralateral brain damage. Despite frequent response extinctions, no concurrent increase in counting errors was observed during bilateral input, indicating that interhemispheric interference in the present case is not equally present in all stages of the input-output chain, but takes the form of an all-or-none rivalry in some gating mechanism. Ancillary findings support different modes of information processing by the two hemispheres, and a possible presence of weak ipsilateral projection of visual information.

Long lasting and changing visual stimuli were used to test peripheral field perception of form, motion and colour in four commissurotomy patients. The stimuli were produced by point source shadow casting or by focused projections on large screens surrounding the subjects, and oculomotor fixation was monitored continuously. It was found that appropriately large and 'active' stimuli in left and right fields were combined by the subjects into unified percepts which they saw as cross integrated over the vertical meridian. In addition, they spoke correctly about attributes of similar stimuli that were confined to the left field. These results were obtained while subjects maintained steady central fixation, and in absence of any acts capable of giving non visual sensory feedback and cross cueing between the hemispheres. It is concluded that ambient vision remains undivided after hemisphere deconnexion, in spite of the complete separation of focal visual perceptions at the vertical meridian caused in these same subjects by the operation. A left handed commissurotomy patient in whom speech was better controlled from the right hemisphere was also examined with the methods described. Implications of these findings for the anatomy of the central visual system of the brain are discussed with the aid of additional observations on a patient with right cerebral cortex removed surgically.

Newly-hatched chicks were given intracranial injections of lithium chloride either before or after being trained in a one-trial passive avoidance task. Twenty minutes after training, memory of the aversive experince was found to be unaffected regardless of the time injections had been given. Retrieval measured 24 hr later, however, was severely impaired in chicks that had been injected 4 min before training, less so in those injected 2 min before, and unaffected in chicks treated 10 sec after training. Thus, while LiCl does not interfere with mnemonic processes necessary for short-term retrieval, it does seem to act with a delayed effectiveness to disrupt an early stage in the development of long-term memory. Previous studies indicate that immediately upon training a metastable memory trace becomes activated which seems to function as behaviorally-retrievable memory for the next hour or so, and which, within the first 45 sec, induces the growth of a behaviorally latent precursor to long-term memory. The present effects of LiCl can be interpreted in these terms as having selectively disrupted formation of the latter precursor component.

Mapping of retinotectal projections in the tree frog Hyla regilla was carried out by both behavioral and electrophysiological recording techniques following tectal ablations, with and without optic nerve regeneration. Scotomata produced by unilateral and bilateral half tectum ablations and by unilateral rectangular midtectal excisions were found to remain essentially unaltered in all cases through recovery periods up to 334 days. Similarly, electrophysiological mapping of the rostral half tectum separated by Gelfilm implants from the caudal tectum for up to 191 days yielded a normal rostral visual field. The stability of the retinotectal projection in adult Hylidae observed in these experiments contrasts with the plastic readjustments obtained in young goldfish in which the retinotectal system is still probably growing and presumably capable of field regulation. The results are taken to support the original explanatory model for developmental patterning of retinotectal connections in terms of selective cytochemical affinities between retinal and tectal neurons.

Interhemispheric interaction after forebrain commissurotomy was studied in six patients. Letters or digits were flashed for 0·1 sec either in the left or in the right visual field alone, or in both fields simultaneously. Patients were asked to identify the stimuli either verbally or by hand. Results showed generally better performance for each hemisphere during unilateral than during bilateral stimulus presentation. For both verbal and manual responses, identification of right-field stimuli was better than that of left-field stimuli, the latter often being completely ignored during bilateral presentations. Some evidence was obtained for right-hemisphere verbalization during unilateral presentation of left-field stimuli.

Commissurotomy patients with surgical disconnection of the cerebral hemispheres offer special advantages for studies involving quantitative and qualitative comparisons between the mental capacities of the 2 hemispheres in that the 2 can be compared directly on the same task in a single individual. In the present study the Raven's Colored Progressive Matrices (RCPM) was modified for lateralized testing in a group of commissurotomy patients. It was administered to a group of patients with surgical section of the cerebral hemispheres in order to compare the independent capacity of left and right hemispheres for spatial apprehension and reasoning. The patterns with missing parts were presented in free vision but the answer had to be sought among a choice of 3 metal-etched patterns in blind tactual exploration using the left and right hands separately. Scores for the 2 hands and speed of performance showed a consistent left hand-right hemisphere superiority, even though the order of presentation was biased in favor of the left hemisphere. Scores for the left hemisphere, however, were well above chance. Results indicate that the test can be performed by either the right or left hemisphere but that the 2 use different strategies of approach and different modes of central processing. (PsycINFO Database Record (c) 2012 APA, all rights reserved)

Behavioral testing for interhemispheric integration in a commissurotomized boy with asymmetric cortical damage indicates a compensatory strengthening in the ipsilateral somesthetic representation of the left hand in the left hemisphere. Unlike previous commissurotomy patients, this subject could name, describe, and locate objects felt by the left as well as the right hand, and could use the left hand to tactually retrieve items, the pictures or names of which had been presented to the right visual field. Evidence was not found for a similar bilateral tactual representation of the right hand. Limited enhancement of language capacities in the minor hemisphere was also found in the form of left handed transcription of printed words into script, and some ability to write and speak about objects in the left hand.

The ability of the disconnected minor hemisphere in two commissurotomy patients to express language was investigated. It was found that words could be expressed via left hand motor mechanisms when stimulus input was confined to the right hemisphere, either by arranging tactually perceivable plastic letters in proper sequence to spell a word or by printing or writing while the left hand was hidden from view. Techniques which minimized possible interference from the major hemisphere resulted in better performance than when such interference was possible, suggesting that at least part of the minor hemisphere;s linguistic deficiences is due to the major hemisphere's dominance over the motor mechanisms for language expression. However, the minor hemisphere also suffers from an intrinsic limitation in linguistic processing as evidenced by its inferiority in writing words as compared with drawing pictures and its inferiority in writing verbs as compared with writing nouns. Our results suggest that though there are two aspects of language expression — central conceptual dominance and peripheral motor dominance — there is a fairly direct relationship between the two. When a hemisphere is intrinsically better equipped to handle some task, its is also easier for that hemisphere to dominate motor pathways.