We see the world as it unfolds in both space and time. Neuroscience research so far, however, has largely focused on the spatial aspects of vision, including orientation and size. No less important to a comprehensive understanding of brain function is an understanding of how visual input is transformed into knowledge about the timing of events in the world. To begin to address this issue, we recorded the activity of single neurons in the frontal eye field (FEF), an area of prefrontal cortex thought to help mediate conscious visual perception. For comparison, we recorded from two portions of the superior colliculus (SC) in the midbrain. The superficial SC receives inputs from the retina and early visual areas, and intermediate SC is associated with early visual processing and the control of eye movements. In two experiments, we measured visual responses to time-varying stimuli and tested whether the magnitudes or latencies of the responses might be used by the brain as a source of timing information.
First, we measured visual responses in individual neurons while two consecutive flashes of light were presented during passive fixation. We found that when stimulus intervals were brief (~200 milliseconds), neurons responded robustly to the first flash but not the second one ("neuronal adaptation"). As intervals lengthened, neurons fired more robustly for the second flash. Thus, information about time was implicit in the size of successive visual responses.
We then asked if this timing information is exploited by the brain. We recorded activity in FEF and SC while monkeys performed a time interval discrimination task. We evaluated the
"magnitude hypothesis", stemming from our adaptation findings, and the "latency hypothesis", which predicts that time intervals are encoded by the relative latencies of visual responses. We found that performance in the task was best described by the magnitude hypothesis; larger visual responses were associated with longer passages of time. We conclude that neuronal adaptation may play a functional role in time perception. Thus, the timing of visual events in the world, at short naturalistic timescales, is partly encoded by the magnitude--not just the latency--of neuronal activity.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-03142011-141157 |
| Date | 30 June 2011 |
| Creators | MAYO, JOSEPH PATRICK |
| Contributors | Marc A. Sommer, James Mazer, Neeraj Gandhi, Aaron Batista, Daniel Simons, Julie Fiez |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-03142011-141157/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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