Task-irrelevant perceptual learning of crossmodal links: specificity and mechanisms
Batson, Melissa Anne
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It is clear that in order to perceive the external environment in its entirety, inputs from multiple sensory systems (i.e. modalities) must be combined with regard to each object in the environment. Humans are highly vision-dependent creatures, with a large portion of the human cortex dedicated to visual perception and many multimodal areas proposed to integrate vision with other modalities. Recent studies of multimodal integration have shown crossmodal facilitation (increased performance at short stimulus onset asynchronies, SOA s) and/or inhibition of return ( IOR ; decreased performance at long SOAs) for detection of a target stimulus in one modality following a location-specific cue in a different modality. It has also been shown that unimodal systems maintain some level of plasticity through adulthood, as revealed through studies of sensory deprivation (i.e. unimodal areas respond to multimodal stimuli), and especially through perceptual learning ( PL )--a well-defined type of cortical plasticity. Few studies have attempted to investigate the specificity and plasticity of crossmodal effects or the contexts in which multimodal processing is necessary for accurate visual perception. This dissertation addresses these unanswered questions of audiovisual ( AV ) crossmodal cuing effects by combining findings from unimodal perceptual learning with those of multimodal cuing effects as follows: (1) the short- and long-term effects of audiovisual crossmodal cuing, as well as the plasticity of these effects were systematically examined using spatially specific audiovisual training to manipulate crossmodal associations using perceptual learning; (2) neural correlates of these plastic crossmodal effects were deduced using monocular viewing tests (discriminating simple and complex stimuli) following monocular and orientation specific crossmodal perceptual training; and (3) psychophysical boundaries of plasticity within and among these mechanisms as dependent on task/training type and difficulty were determined by varying stimulus salience and looking at post-PL changes in response operating characteristics.
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