EVENT: Psychology Colloquium: Prof David Alais (U Sydney)

Psychology Colloquium Tuesday 19th July 4-5pm in Bayliss MCS G.33, followed by post talk drinks (mulled wine?) in the Psychology Courtyard (or, in really bad weather,the Psychology Common Room, 2nd floor of main psychology building)

Presenter: Prof David Alais (U Sydney)

David Alais is Professor of Experimental Psychology at the University of Sydney and runs a busy research laboratory investigating visual and crossmodal perception. After completing his PhD in Sydney, he worked abroad for nine years as a research fellow in the USA, France and Italy, holding fellowships from the Human Frontiers Science Programme and the European Commission before returning to Australia to take up an ARC Australian Research Fellowship and subsequently an ARC QEII Fellowship. David is known for visual research studying how the brain resolves ambiguous or conflicting inputs (in particular 'binocular rivalry') to understand how the brain deals with conflict and selects percepts for conscious perception. Other research focuses on multisensory interactions, examining how the brain combines auditory, visual and tactile information. Two major emphases have been on how the brain optimally combines signals to produce a robust multimodal percept and how it deals with the inevitable temporal asynchronies that arise between sensory modalities.

Title: Serial dependencies in rapid stimulus sequences: Evidence for attractive and repulsive adaptation in multiple sensory modalities

Abstract:

Several recent studies have shown that a rapid form of adaptation occurs between trials in rapid sequences of varying stimuli. Sequential effects often produce positive dependencies (perception biased towards the previous stimulus: similar to priming), contrasting with repulsive aftereffects (negative dependencies) seen after sustained exposure to a single stimulus. Here, a review of very recent work together with new experimental data shows that positive dependencies occur strongly in both spatial and temporal domains, both within and between modalities. Effect sizes can be large, with the previous stimulus accounting for up to a third or more of the current response. These findings suggest a process which stabilises current perception by averaging the recent past to produce the positive dependency. This would be beneficial for any attribute that remains largely stable overtime (discounting variability as noise) but not for highly variable attributes where signal variation conveys important information. For variable attributes, conventional 'repulsive' adaptation provides a better mechanism as it is optimised for detecting change. In experiments that varied the stimulus in two dimensions (one variable attribute, one stable attribute), we found strong dissociation between adaptation effects: a positive dependency for the stable attribute, and a negative one for the variable attributes. The finding that both positive and negative serial dependencies can operate at the same time on the same stimulus suggests a sophisticated flexibility in sensory adaptation.