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  Visual backward masking in rats: A behavioral task for studying the neural mechanisms of visual awareness

Watanabe, M., Totah, N. K., Kaiser, K., Löwe, S., & Logothetis, N. K. (2014). Visual backward masking in rats: A behavioral task for studying the neural mechanisms of visual awareness. Poster presented at 44th Annual Meeting of the Society for Neuroscience (Neuroscience 2014), Washington, DC, USA.

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Watanabe, Masataka1, 2, Author           
Totah, Nelson K1, 2, Author           
Kaiser, K, Author
Löwe, Sindy, Author           
Logothetis, Nikos K1, 2, Author           
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1Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497798              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              

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 Abstract: The neural mechanism of visual awareness has been primarily studied by contrasting neural activity between visible and invisible stimuli, in attempt to unveil the necessary and sufficient condition for neural representations to enter conscious vision. Visual illusions that render stimuli invisible (e.g., binocular rivalry, backward masking) are prominent behavioral paradigms. So far, majority of studies on visual awareness have been conducted on human and non-human primates. Although these studies greatly contributed to establishing specific brain region-dependent modulation of neural activity by awareness, the field would benefit from being able to conduct experiments on rodents. This advance would provide access to modern techniques such as optogenetic manipulation and two-photon imaging, etc. Here, for the first time, we report backward masking in rats. Backward masking is a visual illusion in which a target is rendered invisible by a visual mask that follows the target with a brief stimulus onset asynchrony (SOA). We first developed a head-fixed rat spherical treadmill system that is amicable to rats performing visual tasks with low contrast, short duration stimuli, which are required for testing backward masking. Rats were initially trained to discriminate a “go” target (vertical grating: 0.15cpd, 28deg visual angle) and a “no-go” target (horizontal grating: 0.075 cpd, 28deg visual angle) without the visual mask. They responded either by running or staying still on the treadmill during a brief time-window after stimulus presentation and were rewarded with drops of water for running in response to a “go” target and punished with time-out penalty for running in response to a “no-go” target. Duration and contrast of target stimuli were gradually reduced to experimental parameters for the backward masking experiment (duration:16ms, luminance contrast:15%). After achieving threshold performance (d’ >1.5), backward masking experiments were conducted with SOAs at 16, 33, 49, 66, 83, 99, 116 ms. Plaids were used as visual mask (duration:33ms, luminance contrast:95%). In all 5 rats, smaller SOA led to statistically non-significant differences between hit and false-alarm ratio. In contrast, difference between hit and false alarm rate were significant for larger SOAs. Threshold SOAs at which masking occurred varied across rats (range: 33m -66ms). In conclusion, a visual stimulus can be rendered invisible with short SOAs, and hence, backward masking can be used to study the neural correlate of consciousness in rats.

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 Dates: 2014-11-17
 Publication Status: Issued
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Title: 44th Annual Meeting of the Society for Neuroscience (Neuroscience 2014)
Place of Event: Washington, DC, USA
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Title: 44th Annual Meeting of the Society for Neuroscience (Neuroscience 2014)
Source Genre: Proceedings
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Pages: - Volume / Issue: - Sequence Number: 436.05 Start / End Page: - Identifier: -