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Interocular transfer of learning in horses (Equus caballus)

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  • Equine Research Foundation

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Interocular transfer (IOT) of pattern discriminations was studied in two horses (Equus caballus). An Anglo-Arabian mare and a Paint gelding were monocularly occluded and conditioned to choose the positive stimulus in a simultaneous two-choice discrimination task. When a criterion of ≥ 18/20 correct responses over two consecutive blocks of 20 trials was reached, the trained eye was covered and the stimuli presented to the untrained eye. Testing was continued until criterion was reached with this eye. Four sets of stimuli were presented in this manner. Additionally, two reversal discrimination problems were tested. Stimuli consisted of two-dimensional black patterns on a white background and were presented in a vertical configuration. The horses demonstrated high levels of interocular transfer on the four problems and on the reversal discriminations. The results provide evidence that, contrary to beliefs held by many people, horses are capable of interhemispheric transfer of visual information.
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... Several studies evaluating equine form perception have been conducted [46,[140][141][142][143][144]. In general, these are behavioral studies in which a food reinforcer is used to "chain" a series of behaviors together (e.g., walk into the testing area, look at a visual target, walk up to the target, touch the target, walk back to the stocks for the next trial) that teaches the horse to work independently of the evaluator (Figure 12.30) [41,[140][141][142][143][144]. ...
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The experiments of Myers and Sperry, more than 20 years ago (Myers, 1956; Myers and Sperry, 1953), established the classical procedure for demonstrating interhemispheric transfer of visual information. First, the optic chiasma is transected in the midline; as a result each hemisphere receives information only from the hemianopic field of the ipsilateral eye. The animal is then trained monocularly on a visual discrimination and tested for transfer with the second eye. It is found that if the commissures are intact, learning is usually more rapid with the second eye than the first, provided reward contingencies are also held constant. This is taken to indicate that there is an interhemispheric transfer of information describing both the salient features of the cues and their associations with reward. Much of this chapter will be concerned with evidence for transfer obtained with the use of this method, the essential feature of which is successive monocular training. Although the method has been criticised by Bremer (1972) as unrepresentative of the demands made upon the commissures in intact animals, we shall later see that evidence of interhemispheric interactions obtained under conditions of simultaneous ocular training may be misleading about the capacity of subcortical pathways to handle structured perceptual information.
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