Attenuation of visual search deficits through complimentary tactile stimulation in low luminance environments: evidence from ERP and eye tracking analyses.

Abstract

Event Abstract Back to Event Attenuation of visual search deficits through complimentary tactile stimulation in low luminance environments: evidence from ERP and eye tracking analyses. Mathew Hunter1*, Bettina Olk2 and Ben Godde1 1 Jacobs University, Germany 2 HSD Hochschule Döpfer, University of Applied Sciences, Germany Searching for a visual target among distractors is one of the most common yet complex tasks we are facing in our everyday lives. Despite the fact that our visual search mechanisms are quite adept, we are still subject to limitations of our visual processing which is particularly evident in environments of extremely low luminance (<0.5 cd/m2). Even with a thorough understanding of visual perception in low luminance environments, little is known regarding search processes within these conditions [1], and subsequently, the primary contributing factors to decreases in performance that are observed in these environments and if there are any mechanisms for attenuation. Hunter et al. [2] have provided contrast efficiency functions for simple visual search tasks within the low luminance spectrum, which specifically relate the cumulative effects of relative contrast luminance and the innate contrast of complex target stimuli to search performance. In an attempt to understand the mechanisms behind decreases in performance and how such decreases could be attenuated we have also demonstrated that different aspects of tactile stimulation, such as the predictive probability of a tactile stimulus, or type of tactile stimulation (spatial or frequency information regarding the location of a target), could be used to improve search performance and their fitting along an efficiency function [3]. We suggested a “gating window” providing the psychophysical boundaries pertaining to when in the visual search process tactile information can improve performance, and how this changes with respect to different tactile properties. We observed that coding of a tactile stimulus is only beneficial when a minimum mean response time of 500 ms is required in order to solve the task. The goal of the present study was to assess the neurophysiological mechanisms related to the reception of visual and complimentary tactile information and the visual scanning process. To this end we incorporated measurements of scan patterns (eye tracking) and of event related potentials (ERP). To isolate the temporal determinants of the “gating window”, we specifically focused on the early perceptual components that relate to the visual and tactile reception and integration spanning the first 500 ms of a trial. We targeted seven individual ERP components: P45, N80, P100, N140, N180, N2, and P300 and selected from the Fz, Cz, Pz, C3, C4, P3, P4, O1 and O2 electrodes. Eleven participants performed three different tactile-visual search (target present/absent) paradigms incorporating three different types of tactile encoding, i.e. frequency (20 Hz and 40 Hz stimulation), spatial (left vs right), and frequency and spatial, to provide information regarding the location of a target. We assessed in how far a given type of tactile stimulation was beneficial in improving visual search performance (adapted from [3]). Behavioural results replicated previous findings. The addition of a tactile stimulus designed to provide information about the target, improved performance (RT and d’) which is normally affected in low luminance environments; however, no differences were observed with respect to a specific tactile encoding type. Quantitative analyses of scan patterns measuring the number of saccades, fixation durations, search array dwell time and location were completed. Results revealed that the scan pattern variables were primarily influenced by tactile spatial coding (left vs right) with minimal effects observed in the frequency coding condition. The ERP results primarily implicated the N2 component at Fz, Cz and Pz electrodes as a contributing factor to performance demonstrated by a significant positive correlation with RT (0.87 p < 0.01) and a negative correlation (0.83 p < 0.01) for d’. More specifically, increased peak latencies reflected slower RTs and decreased performance. These correlations remained consistent independent of the type of tactile stimulation. With respect to scanning behavior, the N2 component over the C4 (0.75, p < 0.05) electrode correlated positively with the total number of fixations and negatively with the peak amplitude over the Cz electrode (Cz = -0.67, p < 0.005). The N2 component has been previously implicated in visual tactile cross-modal congruency paradigms [4], where incongruency reflects greater negative potential amplitudes. Consistent with our results, a greater incongruency or conflict would reflect poorer performance (slower RTs and poorer d’ score). Our results provide preliminary evidence with respect to the distinct integration gating component reported by Hunter et al. [3] and ultimately insight into the interactions of multi-sensory integration and performance. The individual components allowed verification of the gating, but more neural processing post this gating process that we did not examine with our study will contribute to response execution.