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Agnieszka Kopinska, Laurence R Harris, Isabel Lee; Comparing central and peripheral events: compensating for neural processing delays. Journal of Vision 2003;3(9):751. doi: https://doi.org/10.1167/3.9.751.
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© ARVO (1962-2015); The Authors (2016-present)
It is well known that different parts of the retina are associated with different processing times. Objects in the periphery are detected long after the same object appearing in the fovea and at different times again if detected by other sensory systems. This is a challenge to perceiving single objects as coherent items when different parts and aspects of the same object might be processed at substantially different rates. Here we measure the relative reaction times to foveal and peripheral visual targets. We compare the difference in reaction times to the delay required for a peripheral target to be perceived as simultaneous with a foveal target.
To measure reaction times, 2 cm diameter circular patches of light were presented unpredictably at either the fovea or 28 degs into the periphery. Spots were presented on a computer CRT display viewed at between 35 cm. Reaction times were measured using key presses. In a separate experiment, using the method of constant stimuli, the same two spots were presented with a delay of from 0–100ms in 10ms steps with either the foveal or peripheral dot coming on first. Subjects reported which light was first and psychometric functions were constructed through the data to determine the point of subjective equality. Viewing was either monocular or binocular.
Reaction times were about 40 ±10 ms faster for spots in the fovea than for spots in the periphery. Simultaneity judgements however were on average within 5 ± 3 ms of veridical. Compensation performance was better when viewing was binocular.
It is perhaps not surprising that things appearing simultaneously at different parts of the retina were perceived as occurring together. But the mechanism by which such huge neural delays are effortlessly and continuously compensated for is intriguing.
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