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Melanie Palomares, Justin Ales, Anthony Norcia; Modulatory effects of attention on the sensitivity to real and implicit motion: a high-density EEG study. Journal of Vision 2009;9(8):902. doi: https://doi.org/10.1167/9.8.902.
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© ARVO (1962-2015); The Authors (2016-present)
When Glass patterns are sequentially presented, they evoke a percept of coherent motion that is often mistaken for real motion. These “dynamic” Glass patterns (dGPs) have little coherent motion energy and the corresponding motion percept has been referred to as being “implicit”. We measured whole-head visual evoked potentials (VEPs) to dGPS and to a nearly identical limited lifetime coherent motion display. Sequential random dot patterns were either spatially offset (implicit motion) or spatiotemporally offset (real motion with lifetime of two frames). The dGPs portrayed a concentric global pattern and the coherent motion displays portrayed rotary motion. The global organizations alternated with randomized versions at 0.83 Hz. The local elements changed at 30 Hz. We evaluated the effect of endogenous attention on VEP responses by asking observers to detect decrements in the coherence of our dot patterns or to perform an unrelated letter identification task near fixation. Responses to the update of the local elements (30 Hz) were slightly larger for real motion than for dGPs, and were not affected by the task. These local responses were restricted to an occipital source. The global responses (0.83 Hz) were larger and sharper for dGPs than for real motion. Directing attention to pattern coherence increased the global response amplitude to implied and real motion by about a factor of two relative to the responses measured during the letter task. These global responses were maximal at more anterior electrodes than the local responses, suggesting extrastriate sources. There was considerable overlap in the scalp topography of the global responses suggesting that dynamic Glass patterns and real motion stimuli activate some of the same cortical areas. Processing in these areas is highly modulated by endogenous attention. Our data further demonstrate that sensitivity local and global structure in implied and real motion is mediated by different mechanisms.
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