Abstract
Recent studies suggested that eye movements are linked to temporal predictability. These studies manipulated predictability by setting the cue-target interval (foreperiod) to be fixed or random throughout the block. Findings showed that pre-target oculomotor behavior was reduced in the fixed relative to the random condition. This effect was interpreted as reflecting the formation of temporal expectation. However, it is unknown whether the effect is driven by target-specific temporal orienting, or rather a result of a more context-dependent state of certainty that participants may experience during blocks with a high predictability rate. In this study we dissociated certainty and orienting in a tilt-discrimination task. In each trial, a temporal cue (fixation color change) was followed by a tilted grating-patch. The foreperiod distribution was varied between blocks to be either fully fixed (same foreperiod in 100% of trials), mostly fixed (80% of trials with one foreperiod and 20% with another) or random (five foreperiods in equal probabilities). The two hypotheses led to different prediction models which were tested against the experimental data. Results were consistent with the orienting hypothesis and inconsistent with the certainty hypothesis, supporting the link between oculomotor inhibition and temporal orienting and its validity as a temporal expectations marker.
Highlights
Recent studies suggested that eye movements are linked to temporal predictability
We found that oculomotor inhibition prior to a predictable target occurs with various types of temporal structures: with rhythmic expectations, when stimuli were predictable because they are part of a rhythmic stream of stimulation[3], and with associative expectations, when targets are rendered predictable by a preceding informative temporal cue in a visual2, auditory[5] or tactile[6] task
To test the prediction of the temporal orienting and the certainty hypotheses, we performed a two-way repeated measures ANOVA on the pre-target saccade rate (SR), with factors Condition and Foreperiod (1 s, 2 s). This analysis revealed a significant interaction between Condition and Foreperiod (F(3, 57) = 6.27, p < 0.001, ηp2 = 0.248, 95% confidence interval (CI) = [0.056, 0.407]), consistent with the temporal orienting hypothesis (Fig. 1B)
Summary
Recent studies suggested that eye movements are linked to temporal predictability. These studies manipulated predictability by setting the cue-target interval (foreperiod) to be fixed or random throughout the block. In our previous studies on oculomotor inhibition, temporal expectation was manipulated by modulating the foreperiod—the time period between a predicting event (e.g. the onset of a temporal cue or the previous stimulus in a stream) and target onset[2,3,5,6] In these studies, we included two conditions: (a) a fixed condition, in which the forepriod was identical for all trials, rendering the target predictable and (b) a random condition, in which it varied between a few options, rendering the target less predictable. It is still an open question whether the oculomotor inhibition effect reflects temporal orienting of attention for specific targets This previously-suggested ‘temporal orienting hypothesis’ is challenged by an alternative ‘certainty hypothesis’, according to which oculomotor inhibition is caused by a general state of elevated certainty in the fixed relative to the random blocks. Of high certainty, the oculomotor system inhibits activity, either because it is prone to be less explorative or due to lower task engagement
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