The study examined the effects of exposure (continuous vs. terminal) and practice (massed vs. distributed) upon prism adaptation, its intermanual transfer, and spontaneous decay. Subjects were measured before and 0, 5, 10, and 15 min. after 30 trials of exposure to 11.3° lateral prism displacement on target-pointing accuracy (each limb separately), placing the arm straight ahead (each limb separately), and setting a pinpoint light source straight ahead. Adaptive pre-post shifts in these measures represented "negative aftereffect," "proprioceptive shift," and "visual shift," respectively. The major findings were that (a) negative aftereffect was greater with distributed than with massed practice, (V) all four groups experienced intermanual transfer of negative aftereffect, (c) proprioceptive shift transferred intermanually for the massed practice but not the distributed practice groups, (d) visual shift occurred only for the distributed practice-terminal exposure group, and (e) both ipsilateral and contralateral negative aftereffect and proprioceptive shift decayed significantly over the 15-min. postexposure period.

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The interaction between vision and audition was investigated using a signal detection method. A light and tone were presented either in the same location or in different locations along the horizontal plane, and the subjects responded with same-different judgments of stimulus location. Three modes of stimulus presentation were used: simultaneous presentation of the light and tone, tone first, and light first. For the latter two conditions, the interstimulus interval was either 0.7 or 2.0 sec. A statistical decision model was developed which distinguished between the perceptual and decision processes. The results analyzed within the framework of this model suggested that the apparent interaction between vision and audition is due to shifts in decision criteria rather than perceptual change.One of the most controversial issues in psychology concerns the genesis of perceptual abilities and the relations that exist among the sense modalities. Until recently. it was strongly believed that "vision is educated by touch." Many scholars, such as Berkeley and Helmholtz. argued that since visual perception is grossly different from the image on the retina, it must be acquired through tactual experience. Although many experiments were conducted to test the cmpirieistie doctrine of visual space perception (e.g., Stratton. 1~97), there has been no unequivocal evidence supporting the position. Indeed, the argument has been challenged by recent studies of intersensory relations. Harris (1965). for example, demonstrated that vision "dominates" and modities the proprioceptive sense when the two modalities arc made to provide discrepant information. Thus. a person viewing the image of his hand through deflecting prism lenses comes to feel his hand where he sees it rather than where it actually is. Rock and Harris (I % 7) reported several experiments which further demonstrated the dominance of vision over touch. They concluded that rather than touch educating vision. the reverse appears to be true.The lind ing of visual dominance over proprioception led other researchers to investigate conflict situat ions involving other sensory modalities. Pick, Wurrcn , and Hay (ll)6l» examined the interaction of vision and proprioception. proprioception and audition. and vision and audition. For vision and audition. the discrepancy was created by displacing

Letter identification in four-letter words, four-letter nonwords, and single-letter displays was tested using a two-alternative, forced-choice procedure. The nonwords were constructed to be pronounceable and orthographically regular. All displays were tachistoscopically presented without pre-or post exposure masking fields. The mean proportions of correct choices were .749 for letters, .735 for words, and .671 for nonwords, with the latter proportion being significantly smaller than those for the other conditions. The relatively high performance for letters was attributed to the absence of masking fields in the present s~u~y, since. masks have ~ee? shown to interfere more with letter processing than word processing in SimIlar studies. The supenorIty of words over regular nonwords was used as evidence to support the hypothesis that the perceptual unit in reading can be at least as large as a four-letter word.

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