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Event Abstract Back to Event Decision making without bounds? Evidence from humans and monkeys Decision making in perceptual classification tasks is generally assumed to depend on accumulation of noisy information. In the reaction time paradigm, behavioral and neurophysiological data support the notion that responses are initiated when a threshold or boundary is reached. However, the termination rule is less conclusive in time-controlled paradigms, where the experimenter controls the timing of the response signal. Two approaches have been used in such cases: 1) At the response cue, a decision is made by comparing the levels of evidence favoring the two choices (Bogacz et. al. 2006, Ratcliff 1978); 2) Alternatively, evidence accumulation may continue only until a bound is reached, and this may occur before response cue onset. If the bound is reached, neural activity and behavioral responses reflect the state of a binary decision variable (Kiani et. al. 2008). We looked at two relevant experiments, one with human participants and the other with monkeys. The human participants saw a rectangle offset to the left or right of fixation and were required to indicate the direction of shift immediately after a response signal that could occur at a delay of 0 to 2000 msec relative to stimulus onset. In the monkey experiment, the stimulus in each trial was coherently moving dots lasting 500 msec. Monkeys were trained to discriminate the motion direction and indicate their decisions by an eye movement after a signal occurring 300-550 msec after the motion termination. In both experiments, a reward cue was presented prior to stimulus onset indicating which response would, if correct, receive a larger reward. For each stimulus condition, we sorted trials into two groups according to the behavioral response latency following the response cue (shorter or longer than the median), and analyzed choices separately for each group. Surprisingly, we found that choices differed systematically between these groups, even for long trial durations in which any hypothesized bound should already have been reached. Human choices were simply less accurate for trials with longer response latencies (5 subjects), whereas monkeys were more biased toward the larger reward option at longer latencies (2 subjects). These effects were observed for trial durations of up to 2.7 seconds in humans, and up to 1.3 seconds in monkeys. These data indicate that decisions in these tasks are not determined solely by a decision variable that crosses a hard bound before receipt of the response cue. Our observations can, however, be accommodated within the framework of the leaky competing accumulator model (Usher & McClelland, 2001) in which the representation of the evidence for each of the alternatives remains unbounded and continuous even after the response signal, with the continuous values influencing both the outcome and the time taken to respond. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Decision making without bounds? Evidence from humans and monkeys. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.189 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Feb 2009; Published Online: 03 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.
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