Local motion effects on form in radial frequency patterns

Abstract

Sinusoidal modulation of radial speed around a circular path of tangentially oriented Gabor patches results in the percept of modulation of the radius. These patterns have been called motion radial frequency (RF) patterns. Sensitivity to these patterns has been attributed to global summation of local speed by mechanisms, analogous to those proposed to explain sensitivity to spatial RF patterns, which are sensitive to particular radial frequencies of speed modulation. We demonstrate that: Adaptation to spatial RF patterns results in a phase specific after effect in motion RF patterns and vice versa; the rate of change of perceived displacement of a Gabor patch with a moving grating with increasing speed of that grating, is independent of whether the patch is or is not incorporated into a circular path; in the absence of local motion direction cues, global integration across 1, 2 and 3 cycles of motion and spatial RF modulation conforms to a power function with the same index; and finally that the magnitude of the motion position illusion is sufficient and necessary to account for sensitivity to motion RF patterns. We therefore propose that motion RF patterns are analyzed by the same mechanisms responsible for sensitivity to spatial RF patterns using perceived rather than actual local positions of the Gabor patches.

Further evidence that local cues to shape in RF patterns are integrated globally

“…Experiment 2 demonstrated that integration of information across cycles is observed for Gaussian windowed RF patterns if the pattern is viewed in sine phase. This result was consistent with the results of other studies that employed closed (Bell & Badcock, 2008;Loffler et al, 2003) or sampled (Dickinson et al, 2010) contours.…”

“…The power function that described the decrease in threshold from one to two and then four cycles of modulation in an RF4 pattern was derived. Given the results of Experiment 1 and several previous studies (Bell & Badcock, 2008;Dickinson et al, 2010;Hess, Wang, & Dakin, 1999;Loffler et al, 2003), the decrease in threshold with increasing numbers of cycles of modulation should be steeper than that predicted by probability summation.…”

“…In this less constrained case, periodic repetition of curvature might be expected to result in integration of signal within the spectrum. Evidence for the integration of repeated shape information around a boundary was provided by the demonstration of rapidly decreasing amplitude thresholds for the detection of sinusoidal modulation of the radius of a circle, as the number of cycles of a particular period of modulation was increased (Bell & Badcock, 2008;Dickinson, Han, Bell, & Badcock, 2010;Loffler, Wilson, & Wilkinson, 2003). If signal is assumed to be a linear function of amplitude of modulation then, for modulation with long periods of modulation (2p/3 or p/2 radians for example), integration of signal around these so called radial frequency (RF) patterns has been shown to be almost linear (the efficiency of integration approaches 100%).…”

The influence of spatial orientation on the perceived path of visual saltatory motion

“…This background produced the percept of an ellipsoid path, with the major axis of the path coinciding with expanding sectors and the minor axis with contracting sectors. These findings were interpreted in line with the observations of De Valois and De Valois (1991) who reported that the perceived position of an object is shifted in the motion direction (though see Dickinson et al, 2010), possibly due to a shift in the receptive field of neurons that code position in the motion direction (see Fu et al, 2002). With the study by Li et al in mind, we questioned whether the curvilinear saltation could be distorted by background motion confined to sectors discretely overlapping with the non-stimulated space between the locations at which elements are presented.…”

“…Finally, we examine whether the perceived curvilinear path of saltation generated by elements of incongruent orientation can be distorted by background motion overlapping the non-stimulated space between the two elements. We reasoned that the neural representation of saltation generated in higher cortical areas would be altered by background motion such that elements perceptually overlapping with the background motion would be shifted in the motion direction (see De Valois & De Valois, 1991;Dickinson, Han, Bell, & Badcock, 2010), leading to a global distortion in the path of motion.…”