Predictiveness of a visual distractor modulates saccadic responses to auditory targets

Saccade landing point selection and the competition account of pro- and antisaccade generation: The involvement of visual attention ? A review

This paper presents a review and summary of experimental findings on the role of attention in the preparation of saccadic eye movements. The focus is on experiments where performance of prosaccades (saccades towards a suddenly appearing item) and antisaccades (saccades of equal amplitude in the direction opposite to where the target moved) is compared. Evidence suggests that these two opposite responses to the same stimulus event entail competition between neural pathways that generate reflexive movements to the target and neural mechanisms involved in inhibiting the reflex and generating a voluntary gaze shift in the opposite direction to the target appearance. Evidence for such a competition account is discussed in light of a large amount of experimental findings and the overall picture clearly indicates that this competition account has great explanatory power when data on saccadic reaction times and error rates are compared for the two types of saccade. The role of attention is also discussed in particular in light of the finding that the withdrawal of attention by a secondary task 200 to 500 ms before the saccade target appears, leads to speeded antisaccades (without a similar increase in error rates), showing that the results do not simply reflect a speed-accuracy trade-off. This result indicates that the tendency for "reflexive" prosaccades is diminished when attention is engaged in a different task. Furthermore, experiments are discussed that show that as the tendency for a reflexive prosaccade is weakened, antisaccades are speeded up, further supporting the competition account of pro- and antisaccade generation. In the light of evidence from neurophysiology of monkeys and humans, a tentative model of pro- and antisaccade generation is proposed.

Combined auditory and visual stimuli facilitate head saccades in the barn owl (Tyto alba)

The barn owl naturally responds to an auditory or visual stimulus in its environment with a quick head turn toward the source. We measured these head saccades evoked by auditory, visual, and simultaneous, co-localized audiovisual stimuli to quantify multisensory interactions in the barn owl. Stimulus levels ranged from near to well above saccadic threshold. In accordance with previous human psychophysical findings, the owl's saccade reaction times (SRTs) and errors to unisensory stimuli were inversely related to stimulus strength. Auditory saccades characteristically had shorter reaction times but were less accurate than visual saccades. Audiovisual trials, over a large range of tested stimulus combinations, had auditory-like SRTs and visual-like errors, suggesting that barn owls are able to use both auditory and visual cues to produce saccades with the shortest possible SRT and greatest accuracy. These results support a model of sensory integration in which the faster modality initiates the saccade and the slower modality remains available to refine saccade trajectory.

Are somatosensory saccades voluntary or reflexive?

The present study examines whether the distinction between voluntary (endogenous) and reflexive (stimulus-elicited) saccades made in the visual modality can be applied to the somatosensory modality. The behavioural characteristics of putative reflexive pro-saccades and voluntary anti-saccades made to visual and somatosensory stimuli were examined. Both visual and somatosensory pro-saccades had much shorter latency than voluntary anti-saccades made in the direction opposite to a peripheral stimulus. Furthermore, erroneous pro-saccades were made towards both visual and somatosensory stimuli on approximately 11-13% of anti-saccade trials. The observed difference in pro- and anti-saccade latency and the presence of pro-saccade errors in the anti-saccade task indicates that a somatosensory stimulus can elicit a form of reflexive saccade comparable to pro-saccades made in the visual modality. It is proposed that a peripheral somatosensory stimulus can elicit a form of reflexive saccade and that somatosensory saccades do not depend exclusively on higher level endogenous control processes for their generation. However, a comparison of the underlying latency distributions and of peak-velocity profiles of saccades made to visual and somatosensory stimuli showed that this distinction may be less clearly defined for the somatosensory modality and that modality-specific differences (such as differences in neural conduction rates) in the underlying oculomotor structures involved in saccade target selection also need to be considered. It is further suggested that a broader conceptualisation of saccades and saccade programming beyond the simple voluntary and reflexive dichotomy, that takes into account the control processes involved in saccade generation for both modalities, may be required.

Interstimulus contingency facilitates saccadic responses in a bimodal go/no-go task

The saccadic response to a suddenly appearing visual target stimulus is faster when an accessory auditory stimulus is presented in its spatiotemporal proximity. This multisensory facilitation of reaction time is usually considered a mandatory bottom-up process. Here, we report that it can be modulated by the predictability of the target location provided by an accessory stimulus, thereby indicating a form of top-down processing. Subjects were asked to make a saccade in the direction of a visual target randomly appearing left or right from fixation. An accessory auditory stimulus was presented either at the same location or opposite to the target, with the probability varying over blocks of presentation. Thus, the auditory stimulus contained probabilistic information about the target location (interstimulus contingency). A certain percentage of the trials were catch trials in which the auditory accompanying stimulus (Experiment 1) or the visual target (Experiment 2) was presented alone and the subjects were asked to withhold their response. In particular with visual catch trials, varying the predictability of target location resulted in reaction time facilitation in the bimodal trials, with both high (80%) and low predictability (20%), but only when both stimuli were presented within a small time window (40 ms). As subjects could not possibly follow the task instructions in this short period explicitly, we conclude that they utilized the interstimulus contingency information implicitly, thus revealing an extremely fast involuntary top-down control on saccadic eye movements.

Cognitive control can modulate intersensory facilitation: speeding up visual antisaccades with an auditory distractor

Although saccadic reaction times to a visual stimulus are facilitated if an auditory accompanying stimulus is presented at the same location, this intersensory facilitation effect (IFE) has not been explored for antisaccades (saccades directed opposite to a visual target). In this study participants were asked to make an antisaccade opposite to a point of light presented right or left of fixation while accompanied by an auditory stimulus either at the same or at the opposite location with different stimulus onset asynchronies. Antisaccade reaction times for unimodal auditory and bimodal stimuli were shorter than for unimodal visual stimulation, in line with prosaccade studies. The auditory accompanying stimulus afforded antisaccade reaction times approximately as fast as prosaccades in the direction of a visual target, especially when it was presented 40 ms before the spatially congruent visual target. Moreover, predictiveness of the target position facilitated performance only when the auditory stimulus was presented at the opposite location and 40 ms before the visual target (interstimulus contingency effect). We conclude that intersensory facilitation is a mandatory, bottom-up process, but in the particular case of a response conflict due to a visual target, IFE can be shown to be modulated by the predictability of the target location.