The Effects Of Controlled Attention On Rhythmic Temporal Expectation

Temporal expectation is the ability to direct attention to a point in time when a relevant event is expected. In general, using explicit or implicit information, such as symbolic cues or temporal regularity of certain events, individuals tend to build up expectation about coming things onset and prepare an optimized response at the appropriate moment in time.Endogenous temporal expectation is built on predictive temporal information given explicitly by symbolic cues and used to voluntarily prepare the response at the expected time. In contrast, temporal expectation can also be induced by the temporal regularities provided by regular sequences of stimuli (called exogenous or rhythmic temporal expectation). And recently, more and more researches have paid attention to dissociating between endogenous and exogenous components. It has been shown that endogenous temporal expectation can be interfered by concurrent working memory task and activate right dorsolateral prefrontal cortex (rDLPFC) which is related to controlled attention. In addition, there are researches dissociating neural mechanism of endogenous and rhythmic temporal expectation. In spite of these findings, there are some researches find that, when subjects are asked pay attention to regular sequences of stimuli, P3b potential reflecting controlled attention is affected. A relevant issue in research on temporal expectation is to determine that whether controlled attention affects rhythmic temporal expectation or not.Experiment 1 constituted a 2×3×2 design with independent variable of Rhythm (regular and irregular) and interval between the end of sequences of stimuli called foreperiod (650ms,950ms and 1250ms) as within participants factor and Task (single and double) as a between participants factor. In both conditions, the temporal preparation task consisted of a sequence of six tones with duration 50ms each and a frequency of 700Hz. This sequence, the interval between tones was 950ms. In the irregular sequence the duration of each interval could be either 350,650,950,1250 or 1550ms. The orders of these five intervals was randomized across trials. Both sequences included the same number of tones and had identical duration, therefore, the only difference concerned temporal regularity or irregularity. Each trial began with the color plus sign, each color selected at random and with the same probability for the memory test. And then a regular or irregular rhythm was presented at random. The rhythm was followed by the target tone, a 100ms sound of 400Hz, that appeared after a foreperiod of variable duration that was generated at random for each trial. Each FP had a different probability of occurrence based on the non-aging distribution. It consisted of increasing the frequency of the shorter foreperiod such that the conditional probability for target appearance remained constant through the trial. The target tone appeared at the 650ms foreperiod in 50% the trials, at the 1100ms foreperiod in 25% of the trials and at the 1400ms foreperiod in 12.5% of the trials. In the remaining 12.5%of the trials, the target tone was not presented (catch trial). In the dual task condition, the procedure was similar to the single-task condition, except for that participants should perform simultaneously a working memory (WM) task. The WM task consisted of remembering how many times each color appeared during a block of trials. At the end of each block. Participant should type how many times a certain color had been presented. Each color was selected at random and with the same probability for the memory test. We hypothesized that, rhythmic temporal expectation was not interfered by the controlled attention, so was simultaneous working memory task. The results showed that participants could predict the moment of target onset on the basis of the regular rhythm and, this ability was not interfered by double task condition.However, there was an issue in Experiment 1. The sequences of stimuli and target tones were both given to participant in auditory. Even in double-task condition, participants might also pay attention to auditory modality to search target tones. To make sure, in Experiment 2, we replaced tone targets with visual targets, with a discriminative reaction time paradigm, in order to make participant pay their attention away from sequences of stimuli. In addition, on account of audition is of higher temporal discriminability than that of vision, we used 350ms,950ms or 1550ms as the interval between sequences of stimuli and visual targets. Others was similar to Experiment 1. The results also showed that participants can make use of regular sequences of sound stimuli to predict visual target onset.These findings support that rhythmic temporal expectation may involve bottom-up process and is not affected by controlled attention.