Combining findings from gaze and electroencephalography recordings to study timing in a visual tracking task Magnus Holth, Audrey L.H. van der Meer and F.R. Ruud van der Weel Electroencephalography (EEG) and gaze data have traditionally been separated in neurocognitive studies because of the artefacts that even small controlled eye movements produce. Study of gaze control in a visual tracking task provides information about an individual’s prospective control. By including gaze events in the EEG analysis, we studied prospective control and its neural correlates during deceleration in a visual tracking task. Adult participants followed with their gaze a small car moving horizontally on a large screen, where the final approach of the car was temporarily occluded, and pushed a button to stop the car at the reappearance point. Two gaze events, the behavioural push button response and the nonbehavioural stimulus onset, were used to time-lock the averaged event-related potential (ERP) waveform. A significant effect of deceleration on peak amplitude in parietal channel Pz (P < 0.05) was found when ERP waveforms were time-locked to the prospective gaze shift over the occluder. The peak decreased in amplitude as car deceleration increased when participants successfully stopped the car, indicating successful deceleration discrimination. No such effect was found when ERP waveforms were time-locked to any of the other events. Thus, a traditional stimulus onset time-locking procedure is likely to distort the averaged signal and consequently hide important Pz-peak amplitude differences on the prospective timing of decelerating object motion during occlusion. This study shows the importance of including behavioural data when studying neural correlates of prospective control and proposes active incorporation of behavioural data into the EEG analysis. NeuroReport 24:968–972  c 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins. NeuroReport 2013, 24:968–972 Keywords: gaze, parietal lobe, prospective control, time-locking averaged electroencephalography, visual motion perception, visual occlusion Developmental Neuroscience Laboratory, Department of Psychology, Norwegian University of Science and Technology, Trondheim, Norway Correspondence to Magnus Holth, MSc, Developmental Neuroscience Laboratory, Department of Psychology, Norwegian University of Science and Technology, 7491 Trondheim, Norway Tel: + 47 735 91960; fax: + 47 735 91920; e-mail: magnus.holth@svt.ntnu.no Received 21 June 2013 accepted 20 August 2013 Introduction The present study is actively combining for the first time gaze and electroencephalography (EEG) recordings in a visual tracking task to study whether human adult participants differentiate between three deceleration conditions. Tracking with the head and eyes a decelerat- ing object that temporarily disappears behind an occluder and that needs to be stopped soon after it reappears requires the ability to estimate and predict the trajectory of the moving object [1]. Prospective control, that is preparing and guiding actions into the future, involves a complex system where perception, action and cognition are tightly coupled together. With objects moving at a constant velocity, time-to-contact (ttc) is given exactly by its first-order estimate (tau) [2]. With objects decelerat- ing or accelerating, the task becomes increasingly complex as humans cannot perceive velocity change as such, but rather the relative change in velocity when it exceeds 20–25% [3]. Port et al. [4] suggested that the challenge of determining the exact ttc with decelerating or accelerating objects can still be solved using tau to determine when to initiate an interceptive action. However, if sensory information is temporarily lost just before the interception, a tau-strategy will result in unavoidable timing errors. Many behavioural studies on prospective control have been carried out, but little is known about the neural correlates for prospective timing [5,6]. It has been shown that gaze behaviour is coupled to interceptive actions with respect to the reappearance of temporarily occluded moving objects [1]. Participants shift their visual atten- tion to the target area well before the reappearance of the occluded object. Multiple brain pathways are involved in the control of eye movements when perceiving visual motion [7]. From studies on nonhuman primates [8] and human adults [9], evidence is emerging that points to the dorsal stream as specialized for visual motion perception, where the general findings are decreased latency and increased amplitude for increasing visual motion velo- city [10]. The dorsal stream, located in humans mostly in the parietal lobe [11], will play an important part in controlling eye movements and interceptive actions when interacting with a moving object [12,13]. Parietal areas of the brain are also suggested to be important for time perception and temporal processing [14,15]. The thres- hold-tau model implies that a certain group of neurons is activated when this threshold is reached [5]. The threshold-tau model is based on a predictive strategy and assumes that the main element of control is when to start the movement [4]. If the threshold is dependent on 968 Visual system 0959-4965  c 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/WNR.0000000000000020 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.