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Munetaka Shidara

Publications and source records attributed to Munetaka Shidara.

5 recordsLinked to original sources
PubMed2005

Effect of visual noise on pattern recognition.

We recognize objects even when they are partially degraded by visual noise. Using monkeys performing a sequential delayed match-to-sample task, we studied the relation between the amount of visual noise (5, 10, 15, 20 or 25%) degrading the eight black and white stimuli used here, and the accuracy and speed with which matching stimuli were identified. The correct response rate decreased slightly as the amount of visual noise increased for both monkeys. Even at the 25% noise level, the correct response rate was more than 80%, indicating that the monkeys can recognize the pattern they are trying to match when the pattern is masked with visual noise. In contrast, the reaction time to the match stimulus increased substantially as the amount of visual noise increased. Thus, the monkeys appear to be trading time to maintain accuracy, suggesting that the monkeys are accumulating information and/or testing hypotheses about whether the test stimulus is likely to be a match for the sample being held in short-term memory.

Animals↗
PubMed2005

Neuronal firing in anterior cingulate neurons changes modes across trials in single states of multitrial reward schedules.

The recorded responses of single neurons often vary considerably in the numbers of spikes emitted across repeats of a single experimental condition. Because of this irregularity and for theoretical convenience the responses are often approximated using a Poisson process. However, it has been frequently pointed out that many details of the responses, including the distribution of spike counts across similar trials, are not consistent with a Poisson process, even an inhomogeneous one. Wiener and Richmond (2003, J Neurosci 23:2394-2406) showed that the spike count distributions could usually be fitted nicely by mixtures of a few (1-3) Poisson distributions, a step they regarded as a computational convenience. Now, we find that a substantial proportion (47%) of the neuronal responses from anterior cingulate cortex, which we conceptualize as part of a system related to the balance between work and reward, have responses with multimodal firing rate distributions. When these distributions are modeled as mixtures of Poisson distributions, the proportions of the different Poisson distributions are related to behavioral state, and might be related to cognitive factors. This suggests that the neurons undergo behaviorally-related mode changes.

Action Potentials↗
PubMed2004

Differential encoding of information about progress through multi-trial reward schedules by three groups of ventral striatal neurons.

In the course of daily activity we continually judge whether the goal sought is worth the work that must be done to obtain it. The ventral striatum is thought to play a central role in making such judgments. When reward schedules are used to investigate these judgments ventral striatum neurons show responses near the time of the cue, the bar-release, and/or the reward delivery. We evaluated the type of coding that occurs at these three time points by using codes or factorizations with: (1) two states for reward versus non-reward, (2) four states for the progress in the reward schedule, and (3) six states for all of the states of the schedule, quantified using information theory and ANOVA. For the bar-release- and reward-related responses the percent variance explained was as high for the two states code as with the six states code. The information for the four state code rose slightly but significantly for the bar-release-related neurons. For the cue-related neurons the code with six states carried more information than the simpler codes. Thus, responses at different times appear to play different roles. Responses occurring early in trials differentiate all states, i.e., the path to a reward, whereas those late in trials code knowledge of impending reward.

Action Potentials↗
PubMed2002

Anterior cingulate: single neuronal signals related to degree of reward expectancy.

As monkeys perform schedules containing several trials with a visual cue indicating reward proximity, their error rates decrease as the number of remaining trials decreases, suggesting that their motivation and/or reward expectancy increases as the reward approaches. About one-third of single neurons recorded in the anterior cingulate cortex of monkeys during these reward schedules had responses that progressively changed strength with reward expectancy, an effect that disappeared when the cue was random. Alterations of this progression could be the basis for the changes from normal that are reported in anterior cingulate population activity for obsessive-compulsive disorder and drug abuse, conditions characterized by disturbances in reward expectancy.

Action Potentials↗