Bimodal Updating Hypothesis

University Of Oregon, Eugene OR

Investigators

Abstract

Project Abstract Objects in nature can be better detected or localized by integrating information across multiple senses. Much of the focus in the literature has been on ?facilitation?, the degree to which, for example, an audiovisual (AV) stimulus evokes responses that are faster or more precise than that achieved with the faster or more precise of the two modalities. The project proposed focuses on a different type of facilitation, first reported in humans, in which performance with bimodal stimuli combines the best features of each modality alone. The applicant?s lab demonstrated a similar result in the barn owl (Tyto alba): An owl turns its head toward auditory targets with shorter latencies but lower precision than toward visual targets. Conversely, head-turns to visual targets take longer to initiate, but are more precise. AV-guided head-turns are both fast and precise, but neither faster nor more precise than to audition and vision, respectively. Correspondingly, neuronal latencies in the owl?s optic tectum (OT), an area involved in the direction of gaze, are shorter for auditory stimuli than for visual stimuli. Conversely, visual spatial receptive fields (SRFs) are finer than auditory SRFs. This novel form of multisensory enhancement will be studied neurophysiologically and behaviorally, guided by the hypothesis that auditory information arrives in the OT first, triggering the head turn. The visual information, arriving later, helps to refine the trajectory of the head turn. Each aim is guided by an organizing question: Aim 1. Do owls update only if later arriving information improves localization or does it update to the later arriving information even at the expense of performance? We will blur the visual component of an AV stimulus to determine whether information from the blurred visual component is incorporated or ignored. Aim 2. Auditory and visual input arrives at the OT with different latencies. What is the delay between the auditory and visual streams beyond which updating is no longer observed? We will test two alternative hypotheses: 1.) Updating is limited by a fixed time window that closes during a saccade, or 2.) Updating requires the temporal overlap between the tectal neural responses to auditory and visual stimuli. To distinguish between these ideas, we will vary the duration of sound as we test various time delays between the auditory and visual components of AV stimuli. Aim 3. Is updating exclusive to multimodal stimuli? A sequential pair of unimodal auditory and visual stimuli will be presented in which the localizability of stimuli are altered to determine whether or not information from both senses is necessary.