Impact of Semantic Relatedness on Associative Memory: An ERP Study

Encoding and retrieval processes in memory for pairs of pictures are thought to be influenced by inter-item similarity and by features of individual items. Using Event-Related Potentials (ERP), we aimed to identify how these processes impact on both the early mid-frontal FN400 and the Late Positive Component (LPC) potentials during associative retrieval of pictures. Twenty young adults undertook a sham task, using an incidental encoding of semantically related and unrelated pairs of drawings. At test, we conducted a recognition task in which participants were asked to identify target identical pairs of pictures, which could be semantically related or unrelated, among new and rearranged pairs. We observed semantic (related and unrelated pairs) and condition effects (old, rearranged and new pairs) on the early mid-frontal potential. First, a lower amplitude was shown for identical and rearranged semantically related pairs, which might reflect a retrieval process driven by semantic cues. Second, among semantically unrelated pairs, we found a larger negativity for identical pairs, compared to rearranged and new ones, suggesting additional retrieval processing that focuses on associative information. We also observed an LPC old/new effect with a mid-parietal and a right occipito-parietal topography for semantically related and unrelated old pairs, demonstrating a recollection phenomenon irrespective of the degree of association. These findings suggest that associative recognition using visual stimuli begins at early stages of retrieval, and differs according to the degree of semantic relatedness among items. However, either strategy may ultimately lead to recollection processes

Electrophysiological correlates of response inhibition and error processing: the effects of strategic manipulation, feedback and traumatic brain injury

Three studies examined the executive functions of sustained attention, behavioral monitoring, response inhibition, and error processing and how these are affected by traumatic brain injury (TBI). All studies used a Go-Nogo task (1) that heavily taxes response-inhibition and monitoring with the use of an improbable Nogo stimulus and constant SOA, and (2) has been found to result in abnormally high error rates in TBI patients. Behavioural and event-related potential (ERP; recorded at 47 electrodes) measures were collected. First, the physiological processes in healthy, young adults were outlined. The predominant "rhythmic" response mode is controlled by the visual stimulus and time-estimation from the preceding response (negative frontal slow wave, FSW). The recognition of the Nogo stimulus is indicated by the posterior N225 that prompts response. The conscious recognition of this inhibition is represented by the fronto-central N300. These processes can be modulated by two feedback mechanisms that serve to "break" the rhythm: (1) monitoring of event-probabilities, P500, and (2) monitoring of errors, Ne/Pe complex. Next, the disordered processes in TBI patients were delineated. The TBI group made more errors than the Control group. The TBI group failed to show the response-related effect in the left frontal region, suggesting deficits in the conscious monitoring of response tendencies. The N300 on Correct Withhold trials was reduced or delayed in the TBI group. In addition, the Ne component (error-detection) was reduced in a group of relatively "acute" TBI patients, while the Pe component (post-detection error processing) was reduced in a group of chronic TBI patients. Finally, because errors can be predicted by RT speed-up, participants were given (a) strategic instructions to slow down, and (b) external feedback (FB) when RTs became to fast. Errors were reduced in the TBI group with strategic instructions and this improvement was maintained by the external FB. ERPs indicated enhanced processing of Speed-FB tones compared to baseline. The Go Response N300, associated with tonic inhibition across all trials, increased with improvements in performance. However, there were no changes in the FSW or the Ne/Pe with these improvements. Improved performance following TBI can be achieved by deliberate slowing facilitated through feedback. (PsycINFO Database Record (c) 2016 APA, all rights reserved)Ph.D

Event-related potentials during learning and recognition of complex pictures

grantor: University of TorontoEvent-related potentials (ERPs) were recorded while subjects learned a large set of complex, coloured pictures. Recognition memory was examined within the same day and after a 24 hour lag. Memory performance decreased from 88% to 65% over 24 hours. The ERP waveforms showed a prominent parietal-occipital P100-N150-P240 complex that was the same in learning and recognition. A centro-parietal P650 wave was larger during recognition than during learning for both the new and old pictures. During learning the pictures elicited a sustained positive potential maximally 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.M.A

Event-related potentials during learning and recognition of complex pictures

grantor: University of TorontoEvent-related potentials (ERPs) were recorded while subjects learned a large set of complex, coloured pictures. Recognition memory was examined within the same day and after a 24 hour lag. Memory performance decreased from 88% to 65% over 24 hours. The ERP waveforms showed a prominent parietal-occipital P100-N150-P240 complex that was the same in learning and recognition. A centro-parietal P650 wave was larger during recognition than during learning for both the new and old pictures. During learning the pictures elicited a sustained positive potential maximally 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.M.A