DETERMINANTS OF MONOCULAR DEPTH CONTRAST

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DESCRIPTION (Adapted from abstract): Many neurological disorders involve the loss of perceptions of spatial abilities, including perceived orientation. Such disorders will often involve deficits in fine motor control involved in manipulating objects in ways appropriate to the spatial constraints imposed by various tasks (e.g., posting a letter). Such deficits are often NOT the result of a loss in binocular stereo vision; that is, they are essentially monocular. The present research is a preliminary attempt to investigate monocular space perception in the pitch dimension. The perception of pitch (inclination about a horizontal axis) will be investigated utilizing a monocular form of Werner's (1937, 1938) "binocular depth contrast" phenomenon. Previously, depth contrast has been investigated as a binocular phenomenon. I have recently found evidence for depth contrast under monocular viewing conditions. The proposed research focuses on three possible bases of the monocular depth contrast (MDC) effect in isolation: (1) Retinal perspective information; (2) Retinal orientation information; (3) Retinal blur information. Further experiments are proposed to examine the relationship of combinations of 'cues'. The first experiment is designed to replicate our previous MDC result under the conditions of the present experiments. Ss will be presented with a test stimulus consisting of 2 luminous test lines in the presence of 2 luminous induction lines, in otherwise complete darkness. The existence of depth contrast will be assessed by the presence of a shift in the physical pitch of the test lines visually perceived as erect (VPE) produced by changes in the pitch of the induction lines. The presence of MDC when the stimulus consists of one test and one induction line (either on the same or opposite sides of the S's median plane) will be used to assess the possibility that the retinal perspective or orientation cue is responsible for MDC. Preliminary results seem to indicate that perspective is not necessary, but retinal orientation in combination with another cue (such as retinal blur) may be responsible for the effect. Comparison of VPE as a function of the physical pitch of the inducing stimulus (under the same conditions as just described to test retinal perspective) with a normally dark-adapted relative to a pilocarpine-induced 'pinhole' pupil will be used to assess the extent to which the gradient of retinal blur produces MDC. Two experiments utilizing the many-to-one mapping of stimulus lines to their retinal projections are proposed to examine the relationship of retinal orientation to the other cue indicated by the preliminary results mentioned above (such as a blur gradient).