Neuronal activity in the monkey prefrontal cortex during a duration discrimination task with visual and auditory cues

To investigate neuronal processing involved in the integration of auditory and visual signals for time perception, we examined neuronal activity in prefrontal cortex (PFC) of macaque monkeys during a duration discrimination task with auditory and visual cues. In the task, two cues were consecutively presented for different durations between 0.2 and 1.8 s. Each cue was either auditory or visual and was followed by a delay period. After the second delay, subjects indicated whether the first or the second cue was longer. Cue- and delay-responsive neurons were found in PFC. Cue-responsive neurons mostly responded to either the auditory or the visual cue, and to either the first or the second cue. The neurons responsive to the first delay showed activity that changed depending on the first cue duration and were mostly sensitive to cue modality. The neurons responsive to the second delay exhibited activity that represented which cue, the first or second cue, was presented longer. Nearly half of this activity representing order-based duration was sensitive to cue modality. These results suggest that temporal information with visual and auditory signals was separately processed in PFC in the early stage of duration discrimination and integrated for the final decision.

Multimodal Integration of Time

Recent studies suggest that the accuracy of duration discrimination for visually presented intervals is strongly impaired by concurrently presented auditory intervals of different duration, but not vice versa. Because these studies rely mostly on accuracy measures, it remains unclear whether this impairment results from changes in perceived duration or rather from a decrease in perceptual sensitivity. We therefore assessed complete psychometric functions in a duration discrimination task to disentangle effects on perceived duration and sensitivity. Specifically, participants compared two empty intervals marked by either visual or auditory pulses. These pulses were either presented unimodally, or accompanied by task-irrelevant pulses in the respective other modality, which defined conflicting intervals of identical, shorter, or longer duration. Participants were instructed to base their temporal judgments solely on the task-relevant modality. Despite this instruction, perceived duration was clearly biased toward the duration of the intervals marked in the task-irrelevant modality. This was not only found for the discrimination of visual intervals, but also, to a lesser extent, for the discrimination of auditory intervals. Discrimination sensitivity, however, was similar between all multimodal conditions, and only improved compared to the presentation of unimodal visual intervals. In a second experiment, evidence for multisensory integration was even found when the task-irrelevant modality did not contain any duration information, thus excluding noncompliant attention allocation as a basis of our results. Our results thus suggest that audiovisual integration of temporally discrepant signals does not impair discrimination sensitivity but rather alters perceived duration, presumably by means of a temporal ventriloquism effect.

Developing a Psychophysical Measure to Assess Duration Discrimination in the Millisecond Range

Duration discrimination in the range of milliseconds is essential for various aspects of behavior and individual differences. The present paper addresses important methodological issues, such as type of stimuli, type of task, method for threshold estimation, and temporal sensitivity of the psychophysical procedure, that should be borne in mind when developing a sensitive and reliable duration discrimination task. Furthermore, it introduces a psychophysical approach for the assessment of individual differences in duration discrimination of extremely brief intervals in the subsecond range. Monte Carlo simulations provide clear evidence that this task is sensitive enough to correctly detect a true difference between temporal stimuli as small as 2 ms with a high probability. Further, the distributional properties of individual performance scores obtained from 534 participants by means of the introduced duration discrimination task are presented.

Regularity Extraction and Application in Dynamic Auditory Stimulus Sequences

Traditional auditory oddball paradigms imply the brain's ability to encode regularities, but are not optimal for investigating the process of regularity establishment. In the present study, a dynamic experimental protocol was developed that simulates a more realistic auditory environment with changing regularities. The dynamic sequences were included in a distraction paradigm in order to study regularity extraction and application. Subjects discriminated the duration of sequentially presented tones. Without relevance to the task, tones repeated or changed in frequency according to a pattern unknown to the subject. When frequency repetitions were broken by a deviating tone, behavioral distraction (prolonged reaction time in the duration discrimination task) was elicited. Moreover, event-related brain potential components indicated deviance detection (mismatch negativity), involuntary attention switches (P3a), and attentional reorientation. These results suggest that regularities were extracted from the dynamic stimulation and were used to predict forthcoming stimuli. The effects were already observed with deviants occurring after as few as two presentations of a standard frequency, that is, violating a just emerging rule. Effects of regularity violation strengthened with the number of standard repetitions. Control stimuli comprising no regularity revealed that the observed effects were due to both improvements in standard processing (benefits of regularity establishment) and deteriorations in deviant processing (costs of regularity violation). Thus, regularities are exploited in two different ways: for an efficient processing of regularity-conforming events as well as for the detection of nonconforming, presumably important events. The present results underline the brain's flexibility in its adaptation to environmental demands.