Abstract
Adults show strong evoked electrical responses to direction_reversing optic flow fields organized in a radial (expansion/contraction) pattern, but weaker responses to rotation or lateral translation (Gilmore et al., 2007). Infants, in contrast, show the strongest evoked responses to lateral translation. Related research shows that adult and infant primates show different space/time tuning functions to global motion (Kiorpes & Movshon, 2004; Hou et al., 2009). In this study, we sought to determine whether adults show the same space/time tuning to different classes of flow patterns. We employed a high_density (128 electrode) montage to record steady_state visual evoked potential (SSVEP) responses to coherence modulations of three optic flow pattern types (left/right translation, rotation, and radial expansion/contraction) at three different speeds (2, 4, and 8 deg/s).Adult participants (n = 17; 11 female) viewed moving dot displays (7 amin dots, 79.4 cd/m2, density = 10%) that modulated in time from incoherent to 100% coherent global motion at 1.2 Hz (1F1). The dot update rate remained constant for all displays (24 Hz, 1F2). Consistent with previous research, responses at the motion coherence modulation frequency (1.2 Hz, 1F1) were largest to radial motion patterns, with peak amplitudes observed over lateral occipital/temporal electrodes. SSVEP amplitudes to rotational and translational patterns were smaller in amplitude overall, with peak amplitudes shown along the occipital midline. The findings suggest that separable cortical networks may process time-varying radial, rotational, and translational optic flow patterns in human adults.