EVENT-RELATED POTENTIALS DURING LEARNING AND RECOGNITION OF COMPLEX PlCTURES Maria Luisa Arrnilio A thesis submitted in conformity with the requirements for the degree of Master's of Arts Graduate Department of Psychology University of Toronto O Copyright by Maria Luisa Armilio, 1997. National Library Bibliothèque nationale l*l of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON K1A ON4 ûttawaON K1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microfonn, vendre des copies de cette thèse sous paper or electronic formats. la foxme de microfiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la prcpnété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni Ia thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. ERPs and Picture Memory Armilio, Maria Luisa Department of Psychology University of Toronto Event-related potentials during leaniing and recognition of complex pictures. Master's Degree, 1997. Event-related potentials (Ems) were recorded while subjects learned a large set of complex, coloured pictures. Recognition memory was examined within the sarne day and after a 24 hour hg. Memory performance decreased From 88% to 65% over 24 hours. The ERP wavefoms showed a prominent parietal-occipital P 100-N 150-P240 complex that was the same in leaming and recognition. A centro-parietal P650 wave was Iarger during recognition than during learning for both the new and old pictures. During learning the pictures elicited a sustained positive potential mavimally recorded in the occipital regions. Finally. in the recognition condition, new pictures elicited an N400 wave over Frontal electrodes while old pictures elicited an earlier centroparietal P650 than novel pictures. Learning is most clearly associated with a sustained occipital positivity. recognition with a parietal positive wave. and novelty-detection with a frontal negative wave. ERPs and Picture Memory Acknowlegements I would like to thank my thesis advisor, Dr. Terence Picton. for his help throughout the preparation of this thesis as well as Dr. Fergus Craik for his suggestions in the design of the expenment and preparation of the written work. Many thanks to Brigitte Boucher and Vincent Choi for their technical expertise, and to those who volunteered their time to participate in the experiment. My research was supported by a University of Toronto Open Fellowship and a Men's Service Group Studentship from Baycrest Centre for Geriatric Care in Toronto. iii ERPs and Picture Memory Table of Contents Page List of Figures .......................................................................................................... v Introduction.............................................................................................................. 1 Method . Participants... ....................................................................................................... Stimuli............................................................................................................... Procedure .......................................................................................................... Results................................................................................................................... Discussion .............................................................................................................. ERPs and Picture Memory List of Figures Figure 1 : Black and white exarnples of the complex, coloured stimuli used in the Experiment. Figure 2: Schema of the procedure employed in the Expenment. Figure 3: Cornparison of grand mean ERP waveforms for new correct and old correct pictures on Day 1 and Day 2. Figure 4: P 100-N150-P240/P350 complex - Potentials consistently evoked by pictures. Figure 5: New vs. Old - The N450 wave. Figure 6: New vs. Old - The P650 wave. Figure 7: Leaming vs. Recognition - The sustained potential. ERPs and Picture Memory 1 Event-related potentiais daring learning and recognition of complex pictures When the psychological study of memory began in the laboratories of Hermann Ebbinghaus in the late 1800's, the centuries-old philosophicai speculation about the mental process called 'memory' became a topic of scientific investigation. In the past 100 years psychoiogists probing the workings of memory have been trying to determine how information gets into memory and how this information is later retrieved. Current opinion suggests that memory consists of many complex systems (Tulving & Schacter, 1990). Information cmbe stored in such systems for durations fiom a fraction of second up to an entire lifetime. The capacity of these memory systems can be as limited as a tiny buffer store or as extensive as the long term memory store that appears to surpass the largest and most powerful cornputers. Whereas hurnans have severe limitations when stonng and retrieving verbal information such as letters, words. nurnbers and sentences, they have an impressive ability to remember complex meaningfùl stimulus configurations such as pictures of people. places and things. Although memory for pictures is extremely enduring and accurate. the physiological bais of this specialized picture memory process has been relatively unexplored. The present study examined the event-related potentials (ERPs) recorded while participants learned and recognized a large set of complex, coloured pictures. More specifically, it addressed the fünction of detecting novel pictures to the hurnan memory process. ERPs and Picture Memory 2 Noveltv Detection Any complex system must be efficient in order to be successful. Since it is uneconomical to store redundant information, it is necessary to decide what incoming information is already in storage and what is not. information that has not yet been experienced should not be overlooked. Thus, novelty detection seems to play a cntical role in deciding what needs to be responded to and stored (Tulving, Markowitsch, Kapur. Habib & Houle, 1994a; Tulving & Kroll. 1995; Tulving, Markowitsch, Craik, Habib & Houle, 1996). Two paramount questions arise: ( 1 ) What areas of the brain are active during novelty detection? and (2) How quickly cmnovelty be determined? The brain imaging technique. positron emission tomography (PET). has successfdly identified areas of the brain that are active dunng novelty detection. Several recent PET studies by Tulving and his colleagues have indicated wide-spread novelty- assessment networks in the brain (Tulving et al.. 1994a; Tulving & Kroll, 1995; Tulving et al., 1996). During recognition tasks involving both verbal and nonverbal stimuli. the most prominent novelty activations occur in cortical and subcortical regions of the right expanded limbic systern - hippocarnpal formation. parahippocampal gyrus. retrosplenial cortex, thalamus. subcallosal area. the border between cortical areas IO and 33 as weil as anterior and inferior cingulate cortex, putamen and media1 prefrontal cortex - and additional activity in various areas of the temporal and temporoparietal lobes bilaterally. These observations have led to the 'novelty-encoding hypothesis'. Specific novelty- assessment networks function to influence whether the encoding of on-line information into long-term memory will take place. Tulving et al. (1996) hypothesize that the encoding of incoming information depends on the novelty of the 'on-line' information. Novelty detection may be accomplished by the neuronal networks in the limbic/temporal regions. These novelty-detecting neurons then activate the lefi-frontal cortical areas that ERPs and Picture Memory 3 have been shown to be involved in the encoding of novel information for episodic memory (Tulving et al, 1994a). While the good spatial resolution of PET can provide information regarding the neuroanatomical areas where novelty detection occurs. it is unabte to answer the second question. that is. how quickly does novelty detection occur? In PET. regional cerebral blood flow is measured for 60 seconds. Thus. data collected from a PET scan provides a composite image of al1 neural activity during that time Me.While information about the neural interactions between different regions can be extracted from PET data through decomposition of interregional covariances of activity to yield a 'network analysis' (e.g.. McIntosh & Godez-Lima 1994), it is impossible to extrapolate back from average blood flow to the time-course of neuronal activity. Thus. while PET can provide answers to the question 'where' novelty detection occurs in the brain. the 'when' question remains unanswered. A usefül tool for addressing the temporal sequence of the processes in novelty detection. and memory in general. is the event-reiated potential or ERP. As the neurons of the human brain process information in cognitive tasks such as leaming and remembering they generate electrical fields. When large numbers of neurons are synchronously active and when the individual fields of these