Abstract
Wallach (1968) argued that certain adaptations of sensory systems can best be understood as adaptive responses to “informational discrepancy”: if two mechanisms estimate the same quantity in the world, but disagree with each other, the system will respond by adjusting the estimators′ biases to equalize the estimates. We have developed a model system for studying this process. The relative disparity between two points in a scene can be measured from their retinal relative disparity (RRD) or from the change in vergence required to fixate them in turn (“delta vergence” or DV). Human observers use both mechanisms (Backus & Matza-Brown, 2003). In the laboratory RRD and DV can be put into conflict, so that they specify different relative disparities. If the conflict persists, one might expect the visual system to recalibrate one or both mechanisms so their estimates agree. The visual system may know that some perceptual mechanisms fall out of calibration more quickly than others, in which case the rate of adaptation should be proportional not only to the estimator′s variance, but also to the rate at which it naturally falls out of calibration (Backus, VSS 2003). RRD is measured directly from the retinal images, so the RRD mechanism could be quite stable over time. However, the DV mechanism depends on the use of controlled eye movements, and eye movements are constantly recalibrated by the visual system. We reasoned that the DV mechanism ought to adapt, perhaps through a change in the vergence component of directed saccades. Observers made depth settings using DV or RRD alone, before and after adaptation. During adaptation, observers nulled depth continuously. The conflict between DV and RRD was increased from 2 to 11 standard deviations of the observer′s null settings, over the course of 10 minutes. There was an effect of adaptation on both the RRD and DV settings, suggesting recalibration within both mechanisms.
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