N2pc Modulation as an Electrophysiological Marker of Output-Based Inhibitory Cueing Effects Sean Skerratt Word count: 9,992 A report submitted as a partial requirement for the degree of Bachelor of Psychology with Honours at the University of Tasmania, 2016 Division of Psychology, School of Medicine University of Tasmania 2016 i Statement of Sources I declare that this report is my own original work and that contributions of others have been duly acknowledged. Date: Sean Skerratt ii Dedication I would like to dedicate the completion of this work to the memory of Liam Burnie. His is a friendship I will not soon forget. iii iv Acknowledgements First and foremost, I would like to thank my supervisor, Dr. Jason Satel. I am sincerely grateful for the continuing guidance and support he has offered throughout the past year. Thanks must also go to Alfred “code-master” Lim, Joel, Jess, and Chelsea whose contributions to this project were invaluable. I would also like to thank my fellow students in the Honours cohort, whose friendship and support over the past year I have greatly appreciated. In particular, my research partner, and paper-toss adversary, Nicholas Wilson. I have enjoyed our time working in the lab this past year, and am thankful for your support, advice, and encouragement. Thanks also go to my employers, for their understanding and flexibility. Lastly, I would like to thank my incredible fiancé Emily, whose unwavering support and love has seen me through, not only this past year, but the entirety of my degree. iv v Table of Contents Statement of Sources .................................................................................................... ii Dedication ................................................................................................................... iii Acknowledgements ..................................................................................................... iv Table of Contents ......................................................................................................... v List of Figures ............................................................................................................ vii Abstract ........................................................................................................................ 1 IOR in Spatial Cueing Tasks ........................................................................................ 3 Inhibitory Cueing Effects ............................................................................................. 4 Input-Based ICEs ......................................................................................................... 5 Output-Based ICE ........................................................................................................ 7 Reconceptualising IOR ................................................................................................ 9 Electrophysiological Markers of ICEs ....................................................................... 10 The P100 Cueing Effect ............................................................................................. 10 Posterior-Contralateral N2 (N2pc) ............................................................................. 12 Attentional Deficits .................................................................................................... 14 Study Rationale & Aims ............................................................................................ 15 Hypotheses ................................................................................................................. 16 Method ....................................................................................................................... 17 Participants ............................................................................................................ 17 Design ..................................................................................................................... 18 Materials ................................................................................................................ 18 Eye tracking. ................................................................................................................................. 18 Electroencephalography ............................................................................................................... 18 Spatial Cueing Task ...................................................................................................................... 18 Procedure ............................................................................................................... 20 Analysis .................................................................................................................. 22 Results ........................................................................................................................ 23 Behavioural Results ................................................................................................ 23 N2pc Results ........................................................................................................... 24 Discussion .................................................................................................................. 26 Behavioural ............................................................................................................ 26 Electrophysiological ............................................................................................... 30 Limitations .............................................................................................................. 35 v vi Future Directions ................................................................................................... 36 Summary and Conclusions ..................................................................................... 37 References .................................................................................................................. 40 Appendix A ............................................................................................................. 49 Appendix B ............................................................................................................. 51 Appendix C ............................................................................................................. 53 Appendix D ............................................................................................................. 54 vi vii List of Figures Figure 1. Example of a typical spatial cueing task ...................................................... 4 Figure 2. Grand mean waveforms showing an N2pc ................................................. 13 Figure 3. Time course of the spatial cueing task used in the present study ............... 20 Figure 4. Mean reaction times for cued and uncued trials across oculomotor-state 24 Figure 6. Grand mean waveforms (uncued-cued) for control in active state ............ 25 Figure 5. Grand mean waveforms (uncued-cued) for control in suppressed state .... 25 Figure 7. Grand mean waveforms (uncued-cued) for deficit in active state ............. 26 Figure 8. Grand mean waveforms (uncued-cued) for deficit in suppressed state ..... 26 vii 1 Abstract An inhibitory cueing effect (ICE) is a phenomenon whereby behavioural responses (such as a manual keypress or saccade) to stimuli appearing at recently attended locations are slowed, provided that time elapsed is sufficient for the extinction of early facilitation effects. This phenomenon, often referred to as inhibition of return (IOR), is thought to be a functional component of visual search which facilitates novelty seeking. Research has demonstrated two dissociable mechanisms underlying ICEs – input-based and output-based. The present study used a modified spatial cueing task with both active and suppressed oculomotor-states, combined with electroencephalography (EEG) measurement, to investigate whether the deployment of covert visual attention (measured as the amplitude of N2pc) is modulated differentially by input and output-based ICEs. Additionally, the present study sought to examine the effect of attentional deficits on both behavioural inhibition (manual response times) and the modulation of deployed attention. Behavioural results showed that ICEs were elicited, however the observed inhibition was identical across oculomotor-state. The effect of group was marginally significant, with post-hoc analyses revealing a significant difference between uncued and cued targets in the control group (slower to cued), but only marginal significance for the deficit group. No significant results were found for N2pc analyses, however a polarity inverse to that expected was observed. Results, interpretations, and recommendations for future research are discussed. 2 Inhibition of return (IOR) is a phenomenon whereby behavioural responses to stimuli appearing at recently attended locations are inhibited, provided that time elapsed is sufficient for the extinction of early facilitation effects (Posner & Cohen, 1984; for a review, see Klein, 2000). It has been conceptualised as an inhibitory mechanism that facilitates novelty seeking in visual search by way of biasing an individual’s attention toward novel salient stimuli (Posner, 1984; Posner, Rafal, Choate, & Vaughan, 1985). From an evolutionary perspective, this inhibition is proposed to have developed as a means by which the detection of task-relevant stimuli