Processing Spatial and Temporal Discontinuities: Electrophysiological Indicators

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Abstract
In a series of four experiments measuring behavioral performance and event-related brain potentials (“ERPs”) in a texture segmentation task, we investigated whether there is evidence that texture stimuli containing a local discontinuity (“D-textures”) are conceptually different from homogeneous stimuli (“H-textures”). Stimuli were presented in an oddball design, with relative frequency of D-textures and H-textures being varied between experiments. It was found that these stimuli are not interchangeable in an oddball situation, as rare D-textures in a context of frequent H-textures give rise to the typical N2b-P3b effects, whereas rare H-textures in a context of frequent D-textures do not. This asymmetry arose because D-textures always elicited enlarged P3b components regardless of their relative frequency. It was concluded that the spatial discontinuity in D-textures adds a feature of “targetness” to these stimuli. Moreover, it was found that a posterior negative-going shift in the N2b latency range (“pN2b”) was mainly modulated by visual stimulus features. This result confirms and extends earlier findings demonstrating the sensitivity of the posterior N2b to physical stimulus characteristics.