The Fixation and Saccade P3 Sangita Dandekar1*¤, Jian Ding 3 , Claudio Privitera3, Thom Carney1,3, Stanley A. Klein1,2,3,4 1 Vision Science Graduate Program, University of California, Berkeley, California, United States of America, 2 Helen Wills Neuroscience Institute, University of California, Berkeley, California, United States of America, 3 School of Optometry, University of California, Berkeley, California, United States of America, 4 Department of Bioengineering, University of California, Berkeley, California, United States of America Abstract Although most instances of object recognition during natural viewing occur in the presence of saccades, the neural correlates of objection recognition have almost exclusively been examined during fixation. Recent studies have indicated that there are post-saccadic modulations of neural activity immediately following eye movement landing; however, whether post-saccadic modulations affect relatively late occurring cognitive components such as the P3 has not been explored. The P3 as conventionally measured at fixation is commonly used in brain computer interfaces, hence characterizing the post- saccadic P3 could aid in the development of improved brain computer interfaces that allow for eye movements. In this study, the P3 observed after saccadic landing was compared to the P3 measured at fixation. No significant differences in P3 start time, temporal persistence, or amplitude were found between fixation and saccade trials. Importantly, sensory neural responses canceled in the target minus distracter comparisons used to identify the P3. Our results indicate that relatively late occurring cognitive neural components such as the P3 are likely less sensitive to post saccadic modulations than sensory neural components and other neural activity occurring shortly after eye movement landing. Furthermore, due to the similarity of the fixation and saccade P3, we conclude that the P3 following saccadic landing could possibly be used as a viable signal in brain computer interfaces allowing for eye movements. Citation: Dandekar S, Ding J, Privitera C, Carney T, Klein SA (2012) The Fixation and Saccade P3. PLoS ONE 7(11): e48761. doi:10.1371/journal.pone.0048761 Editor: Markus Lappe, University of Muenster, Germany Received May 29, 2012; Accepted October 1, 2012; Published November 7, 2012 Copyright: 2012 Dandekar et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Funding for this research was provided by DARPA grant B8U556562 and NIH grant RO1 EY04776. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: sd93@nyu.edu ¤ Current address: Department of Psychology and Center for Neural Science, New York University, New York, New York, United States of America Introduction You are walking down the street when you notice someone waving at you in your peripheral vision. You make an eye movement in the direction of the waving and recognize a friend. Scenarios such as the above, wherein a moment of visual recognition is preceded by a saccade, are quite commonplace. On average, humans make 2–3 saccades a second [1,2] and natural vision is undoubtedly a dynamic, active process. However, most studies of the neural correlates of visual object recognition, and, more specifically of the P3 EEG signal, are conducted in situations in which the subject passively fixates while objects are presented at the fovea. Herein, experiments are presented that attempt to equate visual stimulus characteristics in an object recognition task conducted at fixation and in an object recognition task requiring a saccade. It was hypothesized that the P3 observed after a saccade landing would differ in amplitude, latency and/or persistence from the fixation P3. This hypothesis was based on a variety of past work that demonstrated that visual processing is altered around the time of a saccade, with various past research observing modulations of neural responses and visual perception occurring prior to a saccade [3–5] and post-saccadic modulations of neural activity occurring after saccadic landing [4,6–9]. Saccade related modu- lations in neural activity have been found to be both diverse and complex. For example, recordings in macaque MSTd hint at a complex interplay between modulations of evoked visual responses and modulations of background spontaneous firing rates in the time periods immediately before and after saccades [10]. Interestingly, in the presence of saccades, depending on the presence or absence of visual stimulation, both decreases in BOLD signal as well as increases in BOLD signal have been observed in human LGN and V1 [11]. Furthermore, various groups have hypothesized that object recognition and attention orienting could be enhanced after a saccade due to the known coupling of attention and saccades [12,13]. Based on the post-saccadic modulations described in past studies, it was hypothesized that the saccadic P3 could be enhanced in amplitude and/or decreased in latency relative to the fixation P3. Importantly, past electrophysiological evidence for post-saccadic modulation has mainly been quantified by directly comparing neural activity after a saccade to a baseline level of neural activity measured at fixation. Given that there are a multitude of neural processes that are thought to occur after a saccade but not during fixation (for example, the updating of gaze-centered coordinate systems [14] and the occipital saccadic lambda response [15,16]), the functional role(s) of such post-saccadic modulations remain unclear. In contrast, herein, rather than comparing saccade and fixation neural data directly, we instead compared the difference of the target and distracter post-saccadic neural signals (the saccade P3) and the difference of the target and distracter signals measured at fixation (the fixation P3). Any general changes in neural activity due to the occurrence of a saccade (as well as the EOG artifacts known to co-occur with saccades in EEG) were therefore expected PLOS ONE | www.plosone.org 1 November 2012 | Volume 7 | Issue 11 | e48761