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Amanda Thomas, Rick Gilmore; Temporal and Speed Tuning in Brain Responses to Local and Global Motion Patterns. Journal of Vision 2014;14(10):482. doi: https://doi.org/10.1167/14.10.482.
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Both the detection of local motion speed and direction and the integration of these components into global patterns take time (Burr & Santoro, 2001). Here we investigated the extent to which visual evoked potentials to coherence-modulating radial motion patterns varied as a function of dot lifetime. The goal was to determine the pattern of temporal tuning for local and global motion responses. Radial (expansion/contraction) optic flow patterns elicit robust evoked potential responses in adults (Gilmore et al., 2007). VEP responses also indicate pattern-specific tuning at slow speeds, with lateral occipital areas displaying high activation to radial patterns at slow speeds (Fesi , Thomas, Gilmore, under review). Speed tuning at the dot update rate (F2) and intermodulation harmonics indicated an interaction between global motion coherence and local motion responses. We recorded steady-state visual evoked potential (SSVEP) responses from (n=12) adults with a 128 electrode net. Participants viewed displays depicting a radial expansion/contraction pattern with dots moving at a constant 2 deg/s. Random dot displays (7 amin dots, 79.4 cd/m2, density = 10%) modulated in time from 0% (incoherent) to 100% coherent global motion at .6 Hz, 1.2 Hz, and 2.4Hz (F1). Dot lifetime varied between 83, 167, 333, and 4,160 ms at the dot update rate of 24 Hz (F2). Phase-locked EEG amplitudes at low order integer harmonics (1F1 and 2F1), the dot update rate (1F2: 24 Hz), and intermodulation harmonics (1F2+/-1F1) were analyzed. The highest and lowest modulation frequencies elicited similar activation across channels except at the dot lifetime of 167 ms where strong lateral occipital activation was observed. For all conditions, we replicated the midline occipital activation shown in a previous study at the dot update rate (F2) and the intermodulation harmonics. Results indicate that spatial tuning and the timing of local motion integration varies by coherence modulation frequency.
Meeting abstract presented at VSS 2014
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