Dissociation of local and global contributions to detection of shape with age.

Abstract

Radial Frequency (RF) patterns are a useful stimulus for assessing sensitivity to changes in shape. With these patterns it is possible to separate sensitivity to local curvature information from the ability to globally integrate information around the contour. Previous work has demonstrated that young, school-age children are less sensitive to deformation in RF patterns than adults. However, since the efficiency of contour integration was not assessed, age-related differences in performance could arise from either changes in the strength of global pooling of information, the sensitivity to local curvature information, or both. In this study, psychophysical methods were used to reassess changes in sensitivity to RF patterns, separating changes in sensitivity to local curvature information from changes in contour integration strength. Typically developing observers (aged 6-24, N = 104) were tested using a 2-alternative forced-choice discrimination task with either 1, 2 or 3 cycles of sinusoidal modulation in a pattern of fixed RF. Thresholds were lower for older observers but the rate of change, as more modulation cycles were added, was approximately constant across age. The results indicate that changes in sensitivity to RF3 patterns across age are due to changes in local curvature sensitivity and not to the strength of contour integration. (PsycINFO Database Record

Convergent evidence for global processing of shape

“…Furthermore, there was no evidence of psychometric slopes becoming more shallow with increasing numbers of cycles of modulation (see Figures 8 and 9), a key feature of the SDT probability summation model (Baldwin et al, 2016;Pelli, 1985). In fact, previous research examining the effect of increasing numbers of cycles of modulation on psychometric functions have also found no evidence for a decrease in the slope of the psychometric functions (Baldwin et al, 2016;Cribb, Badcock, Maybery, & Badcock, 2016), further evidence against SDT probability summation for low frequency RF patterns which again, does not rely on summation estimates.…”

Visual search reveals a critical component to shape

“…We predict, therefore, that suprathreshold amplitude RF patterns will be hard to find among rectified RF patterns with the same period and vice versa but, given their demonstrably global processing (Cribb et al, 2016;Dickinson et al, 2012;Green et al, 2017b;Hess et al, 1999;Loffler & Wilson, 2001;Schmidtmann et al, 2012;Tan et al, 2015), RF patterns should be rapidly identified among RF patterns with differing frequency by virtue of the shape cue. Further, RF patterns should be easy to find among circles because of the points of maximum curvature (and concomitant shape cue) they contain, but circles should be hard to find among RF patterns because the absence of these features when the circle is presented among a field of distractors containing them.…”

“…In part, the RF pattern's utility in the study of visual processes arises from a demonstrable integration of shape information around the pattern (Bell & Badcock, 2008;Cribb, Badcock, Maybery, & Badcock, 2016;Dickinson, Han, Bell, & Badcock, 2010;Dickinson, McGinty, Webster, & Badcock, 2012;Green, Dickinson, & Badcock, 2017a, 2017bHess, Wang, & Dakin, 1999;Loffler et al, 2003;Schmidtmann, Kennedy, Orbach, & Loffler, 2012;Tan, Bowden, Dickinson, & Badcock, 2015). When cycles of modulation of a particular frequency are incrementally added to a pattern (with the remainder of the pattern completed by a circular arc) the threshold for discriminating a modulated pattern from a circle decreases at a rate that cannot be accounted for by probability summation-the increase in the probability of detection of single cycles.…”

“…This implies integration of information across cycles of modulation. While a recent study using RF4 patterns of fixed phase or a small set of phases has questioned whether the rate at which threshold decreases can reliably be shown to be greater than the probability summation prediction (Baldwin, Schmidtmann, Kingdom, & Hess, 2016), thresholds for RF3 patterns, and indeed RF4 patterns, in random phase have been consistently shown to decrease almost in inverse proportion to the number of cycles of modulation present on the pattern, reflecting strong integration (Cribb et al, 2016;Dickinson et al, 2012). Furthermore, Dickinson, Bell, and Badcock (2013) have shown that patterns with different frequencies of modulation (RF3 and RF6 patterns) are perfectly discriminated; that is, they can be discriminated at their thresholds for detection of modulation.…”

The effect of spatiotemporal displacement on the integration of shape information

“…The number of channels included (Q) in estimates of probability summation under SDT have a large effect on the resulting predicted strength of integration. Previous research by Cribb, Badcock, Maybery, and Badcock (2016) has used both a ''low'' and ''high'' number of channels to provide an ultra-conservative estimate (low number of channels; Q ¼ 3; and consistent with Baldwin et al, 2016) and a more theoretically appropriate estimate (high number of channels; Q ¼ 120). The same method will be employed by the current study.…”