Deriving the number of salience maps an observer has from the number and quality of concurrent centroid judgments.

[C. Koch, S. Ullman, Hum. Neurobiol.4, 219-227 (1985)] proposed a 2D topographical salience map that took feature-map outputs as its input and represented the importance "saliency" of the feature inputs at each location as a real number. The computation on the map, "winner-take-all," was used to predict action priority. We propose that the same or a similar map is used to compute centroid judgments, the center of a cloud of diverse items. [P. Sun, V. Chu, G. Sperling, Atten. Percept. Psychophys.83, 934-955 (2021)] demonstrated that following a 250-msec exposure of a 24-dot array of 3 intermixed colors, subjects could accurately report the centroid of each dot color, thereby indicating that these subjects had at least three salience maps. Here, we use a postcue, partial-report paradigm to determine how many more salience maps subjects might have. In 11 experiments, subjects viewed 0.3-s flashes of 28 to 32 item arrays composed of M, M = 3,...,8, different features followed by a cue to mouse-click the centroid of items of just the post-cued feature. Ideal detector response analyses show that subjects utilized at least 12 to 17 stimulus items. By determining whether a subject's performance in (M-1)-feature experiments could/could-not predict performance in M-feature experiments, we conclude that one subject has at least 7 and the other two have at least five salience maps. A computational model shows that the primary performance-limiting factors are channel capacity for representing so many concurrently presented groups of items and working-memory capacity for so many computed centroids.

Tapping ahead of time: its association with timing variability.

Researchers have puzzled over the phenomenon in sensorimotor timing that people tend to tap ahead of time. When synchronizing movements (e.g., finger taps) with an external sequence (e.g., a metronome), humans typically tap tens of milliseconds before event onsets, producing the elusive negative asynchrony. Here, we present 24 metronome-tapping data sets from 8 experiments with different experimental settings, showing that less negative asynchrony is associated with lower tapping variability. Further analyses reveal that this negative mean-SD correlation of asynchrony is likely to be observed for sequence types appropriate for synchronization, as indicated by the statistically negative lag 1 autocorrelation of inter-response intervals. The reported findings indicate an association between negative asynchrony and timing variability.

A mechanism of timing variability underlying the association between the mean and SD of asynchrony.

Sensorimotor timing behaviors typically exhibit an elusive phenomenon known as the negative asynchrony. When synchronizing movements (e.g. finger taps) with an external sequence (e.g. a metronome), people's taps precede event onsets by a few tens of milliseconds. We recently reported that asynchrony is less negative in participants with lower asynchrony variability. This indicates an association between negative asynchrony and variability of timing. Here, in 24 metronome-synchronization data sets, we modeled asynchrony series using a sensorimotor synchronization model that accounts for serial dependence of asynchronies. The results showed that the modeling well captured the negative correlation between the mean and SD of asynchrony. The finding suggests that serial dependence in asynchronies is an essential mechanism of timing variability underlying the association between the mean and SD of asynchrony.

Synchronization to a bouncing ball with a realistic motion trajectory.

Daily music experience involves synchronizing movements in time with a perceived periodic beat. It has been established for over a century that beat synchronization is less stable for the visual than for the auditory modality. This auditory advantage of beat synchronization gives rise to the hypotheses that the neural and evolutionary mechanisms underlying beat synchronization are modality-specific. Here, however, we found that synchronization to a periodically bouncing ball with a realistic motion trajectory was not less stable than synchronization to an auditory metronome. This finding challenges the auditory advantage of beat synchronization, and has important implications for the understanding of the biological substrates of beat synchronization.

Attentional modulations of the early and later stages of the neural processing of visual completion.

The brain effortlessly recognizes objects even when the visual information belonging to an object is widely separated, as well demonstrated by the Kanizsa-type illusory contours (ICs), in which a contour is perceived despite the fragments of the contour being separated by gaps. Such large-range visual completion has long been thought to be preattentive, whereas its dependence on top-down influences remains unclear. Here, we report separate modulations by spatial attention and task relevance on the neural activities in response to the ICs. IC-sensitive event-related potentials that were localized to the lateral occipital cortex were modulated by spatial attention at an early processing stage (130-166 ms after stimulus onset) and modulated by task relevance at a later processing stage (234-290 ms). These results not only demonstrate top-down attentional influences on the neural processing of ICs but also elucidate the characteristics of the attentional modulations that occur in different phases of IC processing.