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Mahesh Raj Joshi, Anita J Simmers, Seong Taek Jeon; Limiting Factors in Form and Motion Perception: Shared locally, Differentiated Globally. Journal of Vision 2014;14(10):1418. doi: 10.1167/14.10.1418.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system is functionally differentiated into dorsal (motion) and ventral (form) pathways, owing to the limitations in previously employed stimuli analogous comparison of the outputs from these two streams has proven difficult. In the current study, we adapted the equivalent noise paradigm to (1) disentangle the effect of local and global limits on motion and form perception and (2) compare how those constraints manifest in the two pathways. Six visually normal observers estimated the mean direction or orientation (clockwise or counter-clockwise of vertical) of a field of moving dots (Random Dot Kinematogram; RDK), static dipoles (Glass Pattern; Glass), or dynamic dipoles (dynamic Glass pattern; dGlass) whose direction/orientations were drawn from normal distributions with a range of direction/orientation variances. Thresholds (τ) obtained after five sessions for each stimulus condition showed a consistent pattern across observers and external variance levels, where τGlass>τdGlass>τRDK. Overall, the average threshold ratios between the tasks were constant (1.13, 0.72, and 0.42 log units across external variance levels for τGlass /τRDK, τdGlass/τRDK, and τGlass/τdGlass, respectively), suggesting a parallel vertical shift in performance. This pattern of result was confirmed by the mixed ANOVA where we found significant effect of the external variance (F6.03, 524.37= 185.33, p <.001) and the stimulus type (F2, 87 = 33.50, p <.001), but no interaction between them (F12.05, 524.37= 1.05, p > .1). Nested model comparisons where the thresholds were related to the external variances, internal noise, and the sampling efficiency revealed that change in performance between the tasks can be best described by the sole change in sampling efficiency with the internal noise remained invariable across tasks. Our findings provide a concurrent framework in which to consider global motion and form integration in human perception. This may prove valuable in diagnosing functional visual deficits in a range of developmental/cognitive disorders.
Meeting abstract presented at VSS 2014
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