Saccade trajectory deviations and inhibition-of-return: Measuring the amount of attentional processing

When does “inhibition of return” occur in spatial cueing tasks? Temporally disentangling multiple cue-triggered effects using response history and conditional accuracy analyses

Research on spatial cueing has shown that uninformative cues often facilitate mean response time (RT) performance in valid- compared to invalid-cueing conditions at short cue-target stimulus-onset-asynchronies (SOAs), and robustly generate a reversed or inhibitory cueing effect at longer SOAs that is widely known as inhibition-of-return (IOR). To study the within-trial time course of the IOR and facilitation effects we employ discrete-time hazard and conditional accuracy analyses to analyze the shapes of the RT and accuracy distributions measured in two experimental tasks. Our distributional analyses show that (a) IOR is present only from ~160 ms to ~280 ms after target onset for cue-target SOAs above ~200 ms, (b) facilitation does not precede IOR, but co-occurs with it, (c) the cue-triggered motor response activation is selectively and actively inhibited before target onset, (d) the presence of a central cue causes a temporary negative cueing effect in the conditional accuracy functions, (e) the IOR effect consists of a facilitatory and an inhibitory component when compared to central cueing, and (f) the within-trial time course of IOR is not affected much by the task employed (detection or localization). We conclude that the traditional mean performance measures conceal crucial information on behavioral dynamics in spatial cueing paradigms.

The influence of spatial congruency and movement preparation time on saccade curvature in simultaneous and sequential dual-tasks

Saccade curvature represents a sensitive measure of oculomotor inhibition with saccades curving away from covertly attended locations. Here we investigated whether and how saccade curvature depends on movement preparation time when a perceptual task is performed during or before saccade preparation. Participants performed a dual-task including a visual discrimination task at a cued location and a saccade task to the same location (congruent) or to a different location (incongruent). Additionally, we varied saccade preparation time (time between saccade cue and Go-signal) and the occurrence of the discrimination task (during saccade preparation=simultaneous vs. before saccade preparation=sequential). We found deteriorated perceptual performance in incongruent trials during simultaneous task performance while perceptual performance was unaffected during sequential task performance. Saccade accuracy and precision were deteriorated in incongruent trials during simultaneous and, to a lesser extent, also during sequential task performance. Saccades consistently curved away from covertly attended non-saccade locations. Saccade curvature was unaffected by movement preparation time during simultaneous task performance but decreased and finally vanished with increasing movement preparation time during sequential task performance. Our results indicate that the competing saccade plan to the covertly attended non-saccade location is maintained during simultaneous task performance until the perceptual task is solved while in the sequential condition, in which the discrimination task is solved prior to the saccade task, oculomotor inhibition decays gradually with movement preparation time.

Spatial primes produce dissociated inhibitory effects on saccadic latencies and trajectories

In masked priming, a briefly presented prime can facilitate or inhibit responses to a subsequent target. In most instances, targets with an associated response that is congruent with the prime direction speed up reaction times to the target (a positive compatibility effect; PCE). However, under certain circumstances, slower responses for compatible primes are obtained (a negative compatibility effect; NCE). NCEs can be found when a long pre-target delay is used. During the delay, inhibition is assumed to take place, and therefore an effect on saccade trajectories may also be expected. In a previous study, we found the effects of inhibition on response times and trajectories to be dissociated, but this experiment varied the timing of several aspects of the stimulus sequence and it is therefore unclear what caused the dissociation. In the present study, we varied only one aspect of the timing, but replicated the dissociation. By varying just the pre-target delay, we found a PCE for a short delay, and an NCE for a long delay, but saccade trajectories deviated away from prime directions in both conditions. This suggests dissociated inhibitory effects of primes on response times and saccade trajectories.

Cultural influences on oculomotor inhibition of remote distractors: evidence from saccade trajectories

This study investigated whether low-level attentional processes as indicated by saccade trajectories are modulated by higher-order factors as indicated by participants' cultural background. We hypothesized that if the East Asian participants engage in context-dependent attentional processing to a greater extent than the Western participants, then the magnitude of the distractor effect on saccade trajectories (Doyle & Walker, 2001) should be larger with the East Asian participants than with the Western participants. Participants executed vertical saccades towards targets presented on the vertical meridian above or below fixation. Simultaneously with the target, a distractor appeared in one of the screen quadrants. Consistently with our hypothesis, we found evidence that the saccades of the Chinese participants tended to curve away from the distractors more strongly than the saccades of the German participants. However, this effect was restricted to the upper distractors and the lower targets. The findings are discussed in terms of cross-cultural differences in distractor-related activation and inhibition and functional specialization of hemifields.

Inhibition of masked primes as revealed by saccade curvature

In masked priming, responses are often speeded when primes are similar to targets ('positive compatibility effect'). However, sometimes similarity of prime and target impairs responses ('negative compatibility effect'). A similar distinction has been found for the curvature of saccade trajectories. Here, we test whether the same inhibition processes are involved in the two phenomena, by directly comparing response times and saccade curvature within the same masked priming paradigm. Interestingly, we found a dissociation between the directions of masked priming and saccade curvature, which could indicate that multiple types of inhibition are involved in the suppression of unwanted responses.

Recent advances in the study of saccade trajectory deviations

In recent years, the number of studies that have used deviations of saccade trajectories as a measure has rapidly increased. This review discusses these recent studies and summarizes advances in this field. A division can be made into studies that have used saccade deviations to measure the amount of attention allocated in space and studies that have measured the strength of the activity of a distractor. Saccade deviations have also been used to measure target selection in special populations. Most importantly, recent studies have revealed novel knowledge concerning the spatial tuning and temporal dynamics of target selection in the oculomotor system. Deviations in saccade trajectories have shown to constitute a valuable measure of various processes that control and influence our behavior which can be applied to multiple domains.

Gaze and arrow distractors influence saccade trajectories similarly

Perceiving someone's averted eye-gaze is thought to result in an automatic shift of attention and in the preparation of an oculomotor response in the direction of perceived gaze. Although gaze cues have been regarded as being special in this respect, recent studies have found evidence for automatic attention shifts with nonsocial stimuli, such as arrow cues. Here, we directly compared the effects of social and nonsocial cues on eye movement preparation by examining the modulation of saccade trajectories made in the presence of eye-gaze, arrows, or peripheral distractors. At a short stimulus onset asynchrony (SOA) between the distractor and the target, saccades deviated towards the direction of centrally presented arrow distractors, but away from the peripheral distractors. No significant trajectory deviations were found for gaze distractors. At the longer SOA, saccades deviated away from the direction of the distractor for all three distractor types, but deviations were smaller for the centrally presented gaze and arrow distractors. These effects were independent of whether line-drawings or photos of faces were used and could not be explained by differences in the spatial properties of the peripheral distractor. The results suggest that all three types of distractors (gaze, arrow, peripheral) can induce the automatic programming of an eye movement. Moreover, the findings suggest that gaze and arrow distractors affect oculomotor preparation similarly, whereas peripheral distractors, which are classically regarded as eliciting an automatic shift of attention and an oculomotor response, induce a stronger and faster acting influence on response preparation and the corresponding inhibition of that response.