No reliable effect of task-irrelevant cross-modal statistical regularities on distractor suppression.

Our sensory systems are known to extract and utilize statistical regularities in sensory inputs across space and time for efficient perceptual processing. Past research has shown that participants can utilize statistical regularities of target and distractor stimuli independently within a modality either to enhance the target or to suppress the distractor processing. Utilizing statistical regularities of task-irrelevant stimuli across different modalities also enhances target processing. However, it is not known whether distractor processing can also be suppressed by utilizing statistical regularities of task-irrelevant stimulus of different modalities. In the present study, we investigated whether the spatial (Experiment 1) and non-spatial (Experiment 2) statistical regularities of task-irrelevant auditory stimulus could suppress the salient visual distractor. We used an additional singleton visual search task with two high-probability colour singleton distractor locations. Critically, the spatial location of the high-probability distractor was either predictive (valid trials) or unpredictive (invalid trials) based on the statistical regularities of the task-irrelevant auditory stimulus. The results replicated earlier findings of distractor suppression at high-probability locations compared to the locations where distractors appear with lower probability. However, the results did not show any RT advantage for valid distractor location trials as compared with invalid distractor location trials in both experiments. When tested on whether participants can express awareness of the relationship between specific auditory stimulus and the distractor location, they showed explicit awareness only in Experiment 1. However, an exploratory analysis suggested a possibility of response biases at the awareness testing phase of Experiment 1. Overall, results indicate that irrespective of awareness of the relationship between auditory stimulus and distractor location regularities, there was no reliable influence of task-irrelevant auditory stimulus regularities on distractor suppression.

Temporal Binding in Multisensory and Motor-Sensory Contexts: Toward a Unified Model.

Our senses receive a manifold of sensory signals at any given moment in our daily lives. For a coherent and unified representation of information and precise motor control, our brain needs to temporally bind the signals emanating from a common causal event and segregate others. Traditionally, different mechanisms were proposed for the temporal binding phenomenon in multisensory and motor-sensory contexts. This paper reviews the literature on the temporal binding phenomenon in both multisensory and motor-sensory contexts and suggests future research directions for advancing the field. Moreover, by critically evaluating the recent literature, this paper suggests that common computational principles are responsible for the temporal binding in multisensory and motor-sensory contexts. These computational principles are grounded in the Bayesian framework of uncertainty reduction rooted in the Helmholtzian idea of unconscious causal inference.

Utility of theoretical Hirschberg ratio for gaze position calibration.

PURPOSE: Gaze position is calibrated in first Purkinje image-based eye trackers using the population-average Hirschberg ratio (HR) that is prone to inaccuracies or using the individual's HR that is cumbersome to obtain empirically. This study investigated (1) the agreement between HR calculated theoretically from the individual's corneal curvature and anterior chamber (AC) depth and those obtained empirically and (2) the contribution of corneal curvature and AC depth in the intersubject variance of the two HRs. METHODS: Twenty-four subjects (mean ± SD age, 23.6 ± 3.5 years) fixated monocularly on a light-emitting diode array spanning ±24 degrees of horizontal or vertical gaze angle, in 4-degree steps, at 95 cm viewing distance. Empirical HR was determined using a custom-designed infrared eye tracker as the magnitude of separation between Purkinje image position and entrance pupil center per unit change in angular eccentricity. Theoretical HR was calculated from the subject's corneal curvature and AC depth using the model of Brodie (1987). RESULTS: Empirical and theoretical HRs for horizontal and vertical gaze directions were well correlated (r ≥ 0.83) and not significantly different from each other (p ≥ 0.23; mean difference [±95% limits of agreement], -0.35 [0.85 to -1.55] degrees/mm for horizontal HR and -0.16 [1.01 to -1.33] degrees/mm for vertical HR). Corneal curvature and AC depth together accounted for greater than or equal to 80% and greater than or equal to 91% of intersubject variance in empirical and theoretical HR, respectively (p < 0.001). Hirschberg ratios changed at -2.3 to -2.8 degrees/mm per millimeter change in corneal curvature and at 2.0 to 2.4 degrees/mm per millimeter change in AC depth. CONCLUSIONS: Theoretical HR calculated from the individual's corneal curvature and AC depth can be used in lieu of the empirical HR for gaze position calibration to within approximately 2 degrees/mm of accuracy. Gaze position accuracy significantly improves by using the theoretical HR, relative to the population-average HR. Corneal curvature and AC depth combined explain the majority of intersubject variability in HR.