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The brain constantly adjusts perceived duration based on the recent event history. One such lab phenomenon is subjective time expansion induced in an oddball paradigm (“oddball chronostasis”), where the duration of a distinct item (oddball) appears subjectively longer when embedded in a series of other repeated items (standards). Three hypotheses have been separately proposed but it remains unresolved which or all of them are true: 1) attention prolongs oddball duration, 2) repetition suppression reduces standards duration, and 3) accumulative temporal preparation (anticipation) expedites the perceived item onset so as to lengthen its duration. We thus conducted critical systematic experiments to dissociate the relative contribution of all hypotheses, by orthogonally manipulating sequences types (repeated, ordered, or random) and target serial positions. Participants’ task was to judge whether a target lasts shorter or longer than its reference. The main finding was that a random item sequence still elicited significant chronostasis even though each item was odd. That is, simply being a target draws top-down attention and induces chronostasis. In Experiments 1 (digits) and 2 (orientations), top-down attention explained about half of the effect while saliency/adaptation explained the other half. Additionally, for non-repeated (ordered and random) sequence types, a target with later serial position still elicited stronger chronostasis, favoring a temporal preparation over a repetition suppression account. By contrast, in Experiment 3 (colors), top-down attention was likely the sole factor. Consequently, top-down attention is necessary and sometimes sufficient to explain oddball chronostasis; saliency/adaptation and temporal preparation are contingent factors. These critical boundary conditions revealed in our study serve as quantitative constraints for neural models of duration perception.

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The brightness or color appearance of a region may be altered by the presence of a pattern surrounding it in the visual field. The Munker-White effect (grating surround) and brightness or color induction from concentric annuli ('bull's-eye' surround) are two examples. We examined whether these two phenomena share similar properties. In the asymmetric matching experiment, the task of an observer was to adjust the appearance of a matching patch to match the appearance of a test patch embedded in one of the two types (square wave grating or concentric annuli) of inducing surrounds (inducers). The inducer modulated in one of three color directions (isochromatic: +/-(L + M + S) and isoluminance: +/-(L - M) or +/-S). Each inducer type and color direction had two opposing phases and four contrast levels. The results show that the induced appearance shift increases as a power function of the inducer contrast, regardless of the spatial configuration of the inducer. Further analysis showed that a sensitivity modulation model of lateral interaction could explain both induction effects.

BackgroundParieto-occipital alpha rhythms (8-12 Hz) have been shown to underlie cortical excitability and influence visual performance. However, how the occipital cortex responds to an externally imposed alpha rhythm via transcranial magnetic stimulation (TMS) is an open question.Hypotheses10-Hz rhythmic TMS can entrain intrinsic alpha oscillators in the occipital cortex. Specifically, we predicted: (1) progressive enhancement of entrainment across time windows, (2) output frequency specificity, (3) dependence on the intrinsic oscillation phase, and (4) input frequency specificity to individual alpha frequency (IAF) in the neural signatures.MethodsWe delivered 4-pulse rhythmic TMS at 10 Hz to entrain local neural activity targeting the right V1/V2 regions while participants performed a visual orientation discrimination task.Concurrent electroencephalogram (EEG) recorded TMS-driven changes of local oscillatory activity. There were two control conditions: arrhythmic-active and rhythmic-sham stimulation, both with an equal number of pulses and duration.ResultsThe results were consistent with the first three hypotheses. Relative to both controls, rhythmic TMS bursts significantly entrained local neural activity. Near the stimulation site, evoked oscillation amplitude and inter-trial phase coherence (ITPC) was increased for 2 and 3 cycles, respectively, after the last TMS pulse. Critically, regarding hypothesis 4, ITPC following entrainment positively correlated with IAF, rather than with the degree of similarity between IAF and the input frequency (10 Hz).ConclusionsWe entrained alpha-band activity in occipital cortex for ~3 cycles (~300 ms) with our 4-pulse 10 Hz TMS protocol. IAF predicts the strength of entrained occipital alpha phase synchrony indexed by ITPC.Highlights* online, trial-by-trial entrainment of local neural synchrony in V1/V2 (rhythmic TMS)* occipital entrainment with concurrent neural stimulation (TMS) and recording (EEG)* 4-pulse TMS at 10 Hz yields lasting (300 ms) phase-locking at the alpha-band* individual alpha frequency positively correlated with inter-trial phase coherence