Behavioural and electrophysiological correlates of lightness contrast and assimilation.

Lightness contrast and assimilation are opposite phenomena: in contrast grey targets appear darker when bordering bright rather than dark surfaces; in assimilation grey targets appear lighter when bordering bright rather than dark surfaces. The underlying neurophysiological mechanisms of these phenomena are not known. The aim of this study was to investigate the relationship between contrast and assimilation, and the timing and levels of perceptual and cognitive processing using combined behavioural and electrophysiological methods. Thirty undergraduate students (23 female, age range 18-48 years) participated in a forced-choice (grey target is lighter/darker than a comparison square) task, using stimuli designed such that the inducers were in two configurations (small and large) and two shades (white and black). The behavioural data (more consistent and faster responses) corroborated previous findings of stronger contrast effects with white inducers and stronger assimilation effects with black inducers. According to the Event-Related Potentials (ERP) results the mean amplitude was larger in conditions with less consistent and slower behavioural responses. Thus, with contrast responses P1 amplitude was larger with black than white inducers, and N1 amplitude was larger to assimilation than contrast when the configuration of the stimulus was held constant. These results suggest contrast may occur as early as P1 (~ 110 ms) and assimilation may occur later in N2 (~ 220 ms), whereas in some conditions, differences in ERPs associated with contrast vs assimilation may happen as early as in N1 (~ 170 m), in occipital and parietal cortical sites.

Prioritization of self-relevant perspectives in ageing.

This study investigated whether age-related sensitivity to self-relevance may benefit perspective taking, despite generally poorer perspective-taking capacity in older adults. In one perceptual matching task and two visual perspective-taking paradigms, we examined age differences in sensitivity to avatars representing self and other. In the matching task, older (60-83 years) and younger (18-20 years) adults were similarly biased toward the self- versus other-associated avatar. In the perspective-taking tasks, participants viewed these avatars within a virtual room. Task-relevant perspectives were either the same (i.e., congruent) or different (i.e., incongruent). In the 3PP-3PP task, both avatars were present, and participants adopted the perspective of one or the other. As in the matching task, young and old were similarly biased toward the self-associated avatar. However, age differences emerged in the 1PP-3PP task, which presented only one avatar per trial (varying between self and other), and participants responded based on their own first-person perspective or the avatar's. In summary, age modulated the ability to take perspectives primarily when participants' own first-person perspective was task relevant. Relative to younger adults, older adults prioritized the self (vs. other) avatar more during initial perspective computation and the first-person (vs. third-person) perspective more when selecting between incongruent perspectives.