Exploring the Underlying Mechanisms of the Oddball Effect

This study examines the oddball effect – an illusion of time perception in which an oddball stimulus inserted into a train of temporally matched repeated stimuli appears to last for a relatively exaggerated amount of time (e.g., Eagleman, 2008; Rose & Summers, 1995). This study aimed to determine to what degree, if any, low-level sensory adaptation contributes to the oddball effect. It was predicted that low-level adaptation would not play a role in the oddball effect; rather that the effect would be driven by predictive coding. Two experiments were conducted; both manipulated the style of stimulus presentation (flickering or static) and the eye to which oddball stimuli were presented (same or different relative to other images). Experiment 1 used Troxler fading, which refers to fading with persistent viewing, as a measure of low-level sensory adaptation. These effects were shaped by the eye to which oddballs were shown, but not by the style of stimulus presentation. In contrast, in Experiment 2 it was found that oddball effects are insensitive to eye of origin, but are dependent on intermittent, flickering, stimulus presentations. Overall these data reveal a double dissociation, strongly suggesting that the oddball and Troxler fading effects rely on different causal mechanisms