Characterisation of the Dorsal and Ventral Pathways Using External Noise Paradigm M Joshi, S T Jeon |
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Department of Vision Sciences, Glasgow Caledonian University, United Kingdom
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| Current study evaluated the sensitivity to global motion and form perception which are presumably processed by two distinct visual pathways – dorsal and ventral respectively [Ungerleider and Mishikin, 1982, in: Analysis of Visual Behavior, Cambridge, MIT press] – in varying noise levels. We used Glass pattern [Glass, 1969, Nature, 223, 578-579] and random dot kinematogram (RDK) to evaluate and compare each pathway directly by making the experimental parameters as equivalent as possible in both tasks. Four normal observers discriminated global direction of 500 moving dots or overall orientation of 250 dipoles from 12 o’clock. For each trial, direction/orientation of a dot/dipole was sampled from a normal distribution with one of the eight predetermined direction/orientation variances ranging from ±1° to ±120°, whereas the mean direction/orientation to be discriminated was determined by the 3-down-1-up staircase. When plotted against noise levels, the thresholds remained constant at low variances and started to increase as variance increased. Except for one observer, individual thresholds for Glass pattern were consistently higher than those for RDK across the different variance levels; mean log threshold ratio (Glass/RDK) was 1.503±0.24. In the future, functional mechanisms of both pathways will be quantitatively modelled with consideration of noise. |
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