Naomi Shimizu

Bio: Naomi Shimizu is an academic researcher from University of Hawaii at Manoa. The author has contributed to research in topics: Time perception & Working memory. The author has an hindex of 4, co-authored 4 publications receiving 471 citations. Previous affiliations of Naomi Shimizu include University of California, Berkeley.

Exploring the domain of the cerebellar timing system

Abstract: The ability of an animal to process temporal information has adaptive significance across different temporal ranges. The ability to encode and utilize temporal information allows an animal to predict and anticipate events. However, the time scales vary widely. The predictable event might be based on information that changes over relatively long periods such as a year or a day, or over periods comprising much shorter durations, events that change within a few minutes or milliseconds. Are there a single set of neural mechanisms that are essential for representing temporal information over these different scales? Despite the fact that numerous neural structures have been linked to successful performance on a variety of timing tasks, this question has received relatively little attention. In this chapter, we will focus on the role of the cerebellum in a variety of timing tasks. We will review the hypothesis that the cerebellum can be conceptualized as a relatively task-independent timing mechanism. An important feature of this hypothesis is that the range of the cerebellar timing system is assumed to be relatively restricted. Specifically, we assume that the cerebellum is capable of representing temporal information ranging from a few milliseconds to an upper bound of a few seconds. What remains unclear is whether the cerebellum is involved on tasks spanning longer durations. Cognitive processes such as attention and memory become clearly important here, and indeed, may dominate performance for longer intervals. The animal literature points to non-cerebellar structures as playing a critical role in these tasks and we will provide a brief review of this work. Finally, we will present the preliminary results from two experiments designed to directly test the hypothesis that the cerebellum's temporal capabilities are limited to relatively short durations.

A measurement theory of illusory conjunctions.

Abstract: Illusory conjunctions refer to the incorrect perceptual combination of correctly perceived features, such as color and shape. Research on the phenomenon has been hampered by the lack of a measurement theory that accounts for guessing features, as well as the incorrect combination of correctly perceived features. Recently, several investigators have suggested using multinomial models as a tool for measuring feature integration. The authors examined the adequacy of these models in 2 experiments by testing whether model parameters reflect changes in stimulus factors. In a third experiment, confidence ratings were used as a tool for testing the model. Multinomial models accurately reflected both variations in stimulus factors and observers' trial-by-trial confidence ratings.

Attention alters appearance

Abstract: At any given moment, our visual system is confronted with far more information than it can process effectively. The high energy cost of neuronal activity involved in cortical computation severely limits our capacity to process this information 1 .V isual attention serves as a mediating mechanism, enabling us to selectively grant priority of processing to certain aspects of the visual scene. One means of granting priority is to direct one’s gaze towards the relevant location. However, many situations call for one to attend to an area in the periphery without actually directing gaze toward it. For example, when driving it is generally best to keep your eyes on the road ahead while covertly monitoring the periphery for cars, pedestrians and potential road hazards. The impact of covert attention 2 on visual performance is well-documented across a range of perceptual tasks, such as visual search 3‐6 ,l etter identification 7,8 ,c ontrast sensitivity 9‐12 and spatial resolution 13‐16 .S everal studies that used single-cell recording 17‐22 ,e vent-related potentials 23,24 and functional magnetic resonance imaging (fMRI) 25‐27 indicate that attentional modulation

The evolution of brain activation during temporal processing.

Abstract: Timing is crucial to many aspects of human performance. To better understand its neural underpinnings, we used event-related fMRI to examine the time course of activation associated with different components of a time perception task. We distinguished systems associated with encoding time intervals from those related to comparing intervals and implementing a response. Activation in the basal ganglia occurred early, and was uniquely associated with encoding time intervals, whereas cerebellar activation unfolded late, suggesting an involvement in processes other than explicit timing. Early cortical activation associated with encoding of time intervals was observed in the right inferior parietal cortex and bilateral premotor cortex, implicating these systems in attention and temporary maintenance of intervals. Late activation in the right dorsolateral prefrontal cortex emerged during comparison of time intervals. Our results illustrate a dynamic network of cortical-subcortical activation associated with different components of temporal information processing.

Rhythm and Beat Perception in Motor Areas of the Brain

Abstract: When we listen to rhythm, we often move spontaneously to the beat. This movement may result from processing of the beat by motor areas. Previous studies have shown that several motor areas respond when attending to rhythms. Here we investigate whether specific motor regions respond to beat in rhythm. We predicted that the basal ganglia and supplementary motor area (SMA) would respond in the presence of a regular beat. To establish what rhythm properties induce a beat, we asked subjects to reproduce different types of rhythmic sequences. Improved reproduction was observed for one rhythm type, which had integer ratio relationships between its intervals and regular perceptual accents. A subsequent functional magnetic resonance imaging study found that these rhythms also elicited higher activity in the basal ganglia and SMA. This finding was consistent across different levels of musical training, although musicians showed activation increases unrelated to rhythm type in the premotor cortex, cerebellum, and SMAs (pre-SMA and SMA). We conclude that, in addition to their role in movement production, the basal ganglia and SMAs may mediate beat perception.