Steady-State Visually Evoked Potential Correlates of Object Recognition Memory
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Steady-State Visually Evoked Potential Correlates of Object Recognition Memory Thesis for Doctorate of Philosophy Andrew Pipingas, BAppSc(Dist) February, 2003 Brain Sciences Institute, Swinburne University of Technology Declaration This thesis contains no material which has been accepted for the award of any other degree at any University and to the best of my knowledge and belief contains no material previously published or written by another person or persons except where due reference is made. Andrew Pipingas February, 2003 Acknowledgements The author would like to acknowledge the following people whose contribution made this work possible. My supervisor and mentor, Prof. Richard Silberstein, for his invaluable assistance, guidance and patience throughout the project and for providing me with the intellectual inspiration to undertake a PhD project in the area of brain electrophysiology. Mr David Simpson for the design and development of the instrumentation used to conduct this work and for his assistance with many other computer-related and technical matters. Mr Geoff Nield for his assistance with the development of a suite of software programs that were used to analyse the data. Ms Barbara Livett for generously giving up so much time to assist with various drafts and the English expression for this thesis. Assoc. Prof. Aina Puce and Assoc. Prof. David Crewther for their helpful comments on earlier drafts of the manuscript. My parents for providing me with the motivation and support to pursue a higher degree and, together with my brother, for providing continual encouragement and support. Finally, I would like to thank my wife and daughter for their encouragement, support and patience during the highs and lows associated with a PhD project. Contents List of figures.................................................................................................................... v List of equations .............................................................................................................vii List of abbreviations and units .....................................................................................viii Abstract............................................................................................................................ix Chapter 1 Introduction..............................................................................................1 Chapter 2 Neural correlates of object recognition memory.....................................8 2.1 Object recognition memory: a brief overview..............................................9 2.1.1 Inferotemporal cortex and primate studies of object recognition .............9 2.1.2 The temporal lobes and object recognition memory in human and other primates .................................................................................................................13 2.1.3 A brief summary of haemodynamic (PET and fMRI) neuroimaging correlates of episodic memory retrieval..................................................................18 2.2 Human electrophysiological correlates of episodic memory retrieval .....21 2.2.1 EEG and ERP functional electrophysiological techniques: a brief background..............................................................................................................22 2.2.2 EEG changes associated with episodic memory retrieval.......................25 2.2.3 Event-related potential changes associated with episodic memory retrieval .................................................................................................................32 2.2.3.1 ERP correlates of episodic memory retrieval: evidence from continuous recognition paradigms ......................................................................32 2.2.3.2 ERP correlates of episodic memory retrieval: evidence from study-test paradigms ............................................................................................................41 2.2.3.3 Differentiation between transient item-related and sustained task- related ERP correlates of episodic memory retrieval..........................................56 2.3 Summary of neural correlates of object recognition memory ..................58 Chapter 3 Steady-State Probe Topography ............................................................62 i 3.1 Steady-state evoked potentials compared with transient evoked potentials .........................................................................................................................62 3.2 Steady-state evoked potentials in the study of cognitive processes...........64 3.3 Steady-State Probe Topography (SSPT).....................................................65 3.4 SSPT and recording artifacts.......................................................................70 3.5 Overview of investigations utilizing the SSPT technique ..........................70 3.5.1 Visual vigilance.......................................................................................72 3.5.2 Planning - Wisconsin Card Sorting Task................................................73 3.5.3 Attention - Continuous Performance Task..............................................74 3.5.4 Clinical application of SSPT - ADHD....................................................74 3.5.5 Spatial working memory.........................................................................75 3.6 Conclusions ....................................................................................................76 3.7 Formulation of hypotheses for the present investigation ..........................76 Chapter 4 Methods ..................................................................................................79 4.1 Introduction...................................................................................................79 4.2 Cognitive task design ....................................................................................80 4.3 Task presentation and stimulus parameters ..............................................83 4.4 Subjects ..........................................................................................................84 4.5 Probe stimulus ...............................................................................................85 4.6 Recording.......................................................................................................86 4.6.1 Electrodes and recording setup ...............................................................87 4.6.2 Recording instrumentation and phase locked data acquisition ...............88 4.7 Analysis of behavioural data........................................................................90 4.8 Offline signal processing...............................................................................90 4.8.1 Extraction of the 13Hz SSVEP from the EEG signal .............................90 4.8.2 Automatic detection of artifact in the EEG signal ..................................92 4.8.3 Calculations for modal and transient effects...........................................93 4.8.3.1 Long averaging period (sustained effects) ..........................................94 4.8.3.2 Short averaging period (transient changes).........................................94 ii 4.8.4 Group averaging......................................................................................96 4.8.4.1 Group averaging: long averaging period (sustained effects) ..............97 4.8.4.2 Group averaging: short averaging period (transient changes) ............98 4.8.5 Topographic mapping of SSVEP data ..................................................100 4.8.6 Statistical analysis and Significance Probability Mapping ...................101 Chapter 5 Results...................................................................................................103 5.1 Behavioural data .........................................................................................104 5.1.1 Individual subject..................................................................................104 5.1.2 Group data.............................................................................................105 5.2 Electrophysiological data ...........................................................................107 5.2.1 Sustained effects: long averaging period ..............................................107 5.2.1.1 Individual subjects ............................................................................107 5.2.1.2 Group data.........................................................................................109 5.2.2 Transient changes: short averaging period............................................113 5.2.2.1 Changes with memory load...............................................................114 5.2.2.2 Targets versus non-targets.................................................................124 Chapter 6 Discussion.............................................................................................128 6.1 Behavioural results: the effect of increasing memory load on retrieval accuracy and response time ...................................................................................128 6.2 Sustained SSVEP amplitude and latency changes and retrieval mode..130 6.2.1 The topography of sustained SSVEP changes ......................................131 6.2.2 Interpretation of sustained SSVEP amplitude and latency reductions..134 6.3 Transient SSVEP amplitude and latency changes: the effect of memory load on successful memory retrieval