Abstract
Signal detection theory (SDT) established in psychophysics a crucial distinction between sensitivity (or discriminability, d’) and bias (or criterion) in the analysis of performance in sensory judgement tasks. SDT itself is agnostic about the origins of the criterion, but there seems to be a broad consensus favouring ‘response bias’ or ‘decision bias’. And yet, perceptual biases exist and are readily induced. The motion aftereffect is undoubtedly perceptual - compelling motion is seen on a stationary pattern - but its signature in psychophysical data is a shift in the psychometric function, indistinguishable from ‘response bias’. How might we tell the difference? I shall discuss these issues in relation to some recent experiments and modelling of adaptation to blur (Elliott, Georgeson & Webster, 2011). A solution might lie in dropping any hard distinction between perceptual shifts and decision biases. Perceptual mechanisms make low-level decisions. Sensory, perceptual and response criteria might be represented neurally in similar ways at different levels of the visual hierarchy, by biasing signals that are set by the task and by the history of stimuli and responses (Treisman & Williams, 1984). The degree of spatial localization over which the bias occurs might reflect its level in the visual hierarchy. Thus, given enough data, the dilemma (are aftereffects perceptual or due to response bias?) might be resolved in favour of such a multi-level model.
Meeting abstract presented at VSS 2012