The effects of aging on contour discrimination in clutter

Abstract

The present study examined the effect of aging on the detection and discrimination of contours embedded in a dense field of distractors. The minimum stimulus duration required to correctly discriminate (Experiment 1) and detect (Experiment 2) three types of "C" shaped contours was measured. Overall, older subjects required longer stimulus durations than younger subjects in all conditions. Comparing performance for contours comprising elements oriented tangentially to the contour path (aligned) and those oriented orthogonally to the contour (radial) revealed that the effect of local orientation on contour discrimination is slightly greater in older than younger subjects. Control experiments showed that these age differences were not due to differences in retinal illuminance, or the detectability or discriminability of the elements comprising the contours. These findings suggest that ability to extract global contours embedded in clutter declines in older age.

Aging and the integration of orientation and position in shape perception

“…Interelement spacing has also been shown to affect the detectability and discriminability of elongated contours embedded in cluttered backgrounds (e.g., Beaudot & Mullen, 2003;Kovács & Julesz, 1993;Li & Gilbert, 2002). Interestingly, similar to the current results, the effect of interelement spacing on contour grouping was the same in younger and older subjects (Hadad, 2012;Roudaia et al, 2013), even though overall ability to detect and discriminate contours in noise declines with aging (Del Viva & Agostini, 2007;Roudaia et al, 2011Roudaia et al, , 2013. Although Day and Loffler (2009) speculated that the shape illusion is generated by integration by a global pooling mechanism, as opposed to local contour integration mechanisms thought to underlie detection of elongated contours in noise (e.g., Field, Hayes, & Hess, 1993), there is growing evidence suggesting that global shape mechanisms do not operate directly on individual contour elements, but instead pool information from intermediate-stage mechanisms that integrate local orientation information to encode curved contour segments and inflection points (e.g., Bell et al, 2011;Bell, Hancock, Kingdom, & Peirce, 2010;Kempgens et al, 2013;Schmidtmann et al, 2012).…”

“…The stimulus duration was chosen to match previous studies, as well as to preclude any eye movements when performing the shape judgments. In a previous study, we showed that reducing stimulus duration to 40 ms does not have a differential effect on older subjects' orientation discrimination thresholds for single Gabors (Roudaia et al, 2011), andHabak et al (2009) showed that younger and older subjects' radial modulation thresholds for RF5 contours are equally affected by changes in stimulus duration over a range from 40-500 ms. Thus, the current results are likely to generalize to longer stimulus durations.…”

“…Although these neurophysiological changes would be expected to produce noticeable declines in pattern vision with aging, studies in older humans have found no evidence of broader orientation or spatial frequency tuning with aging (Delahunt,Allard, & Faubert, 2007), bilateral symmetry detection (Herbert, Overbury, Singh, & Faubert, 2002), perceptual grouping (Kurylo, 2006), perceptual contour completion (Richards, Bennett, & Sekuler, 2006;Salthouse & Prill, 1988), and figure-ground segregation (Lass, Bennett, Peterson, & Sekuler, 2012). For example, when discriminating sampled contours, older subjects are significantly more affected by the addition of cluttering elements (Casco, Robol, Barollo, & Cansino, 2011), or by increases in the relative spacing of contour and noise elements (Del Viva & Agostini, 2007;Roudaia et al, 2013), and require longer stimulus durations to reach the same performance level as younger subjects (Roudaia, Farber, Bennett, & Sekuler, 2011). At the same time, disruptions in collinearity of contour elements and changes in contour element proximity have a similar effect on younger and older subjects (Hadad, 2012;McKendrick et al, 2010;Roudaia et al, 2013).…”

Visual Form Perception from Age 20 through 80 Years

“…There are previous reports of differences in mean performance between younger (typically aged below 35 years) and older (typically aged above 60 years) groups for all the tasks included in our study (collinear facilitation, 16 centersurround suppression, 18,19 contour integration, [21][22][23]38 Glass pattern coherence thresholds 24 ). In this dataset, the main effect of group approached significance for the collinear facilitation task and the contour integration tasks.…”

“…18,19 The ability to detect and discriminate contours comprised of local elements declines 20 and is more susceptible to the effects of surrounding clutter. [21][22][23] Age-related differences exist in the perception of shapes defined by texture, 24 and for higher levels of form processing, such as facial matching when faces are displayed from different viewpoints. 25 Previous studies that have documented age-related changes to form perception generally have included two age groups: younger adults (usually below ages 35 to 40 years) and older adults (typically over the age of 60 years), and have conducted detailed experiments on a specific aspect of form perception (e.g., orientation discrimination, 12 center-surround suppression of perceived contrast, 18,19 contour integration, 22 shape discrimination 26 ).…”