Generalization And Discrimination In The Conditioned Eyelid Response To Sound Stimuli

Author : Lee Shalev
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (129 download)

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Download or read book The Effect of Visual Aversive Learning on Generalization written by Lee Shalev and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent studies demonstrated that aversive learning can modulate perceptual thresholds that contribute to later over-generalization. This effect was demonstrated in various modalities, and mainly in the auditory domain. However, the effect of visual aversive stimuli on discrimination, particularly for basic features of visual perception, has been less studied. It remains unclear if this effect is a specific property of the auditory domain, driven by its specialized connectivity with the amygdala, or alternatively, a general characteristic of aversive learning. Examining this question in the visual domain is of major importance. First, it can provide robustness to the suggestion that aversive stimuli induce plasticity in early sensory regions via a central mechanism, independent of the specific input modality. Second, due to the obvious prevalence of the visual system in humans, and its contribution to the development of anxiety states, such findings can reinforce the notion that perceptual mechanisms play a role in the over-generalization observed in anxiety-disorders. In my work I tested the role of the visual system in over-generalization in a series of five studies. In all experiments participants learned to associate auditory or visual neutral stimuli (the conditioned stimuli, CST) with aversive images (the unconditioned stimuli, UST). The effect of this pairing on auditory or visual discrimination thresholds was examined and compared to unpaired stimuli or to pairing with neutral images. I used pupil size and eye movement measurements as indicators for participants' aversive feeling and emotional arousal during learning. In addition, I used functional imaging (fMRI) to track brain activations associated with conditioning. I hypothesized that aversive images would induce an increase in discrimination thresholds for both auditory (tone-frequency) and visual (contrast and orientation) features, accompanied by differences in pupil size, eye movement patterns, and brain activity, measured during aversive visual learning. I further predicted that early visual regions would show activation for neutral stimuli, which acquire aversive value. I found higher discrimination thresholds for both modalities, auditory and visual, and for two features of the visual domain - orientation and contrast. The increased thresholds indicate that participants deteriorated in their discrimination performance (generalization), compared to their baseline abilities and compared to control. The change was stimulus specific and lasted for at least 24 hours. I measured larger pupil size during aversive, compared to neutral image presentation. Additionally, eye movement patterns measurements revealed lower average fixation duration and higher average saccade amplitudes during aversive compared to neutral image presentation. The results were paralleled with increased neural activations during aversive learning in regions that were previously associated with fear conditioning. These regions include the amygdala, insula, and anterior cingulate cortex (ACC). Activity in the insula and ACC was measured even during non-reinforced trials, where the neutral conditioned stimulus was not followed by aversive stimuli. The ventral occipital temporal cortex (vOTC) was also more active during aversive learning trials compared to neutral trials. Remarkably, higher brain activations in the early visual cortex was also observed during non-reinforced trials. This activity was measured in aversive compared to neutral non-reinforced trials, despite the fact that the visual information in these two conditions was identical. My findings suggest that the brain might utilize a central multi-modal mechanism, which modulates early perceptual properties following exposure to negative situations. Such plasticity can contribute to abnormal responses that underlie anxiety states, even in new and safe environments. -- abstract.