Basic perceptual changes that alter meaning and neural correlates of recognition memory

It is difficult to pinpoint the border between perceptual and conceptual processing, despite their treatment as distinct entities in many studies of recognition memory. For instance, alteration of simple perceptual characteristics of a stimulus can radically change meaning, such as the color of bread changing from white to green. We sought to better understand the role of perceptual and conceptual processing in memory by identifying the effects of changing a basic perceptual feature (color) on behavioral and neural correlates of memory in circumstances when this change would be expected to either change the meaning of a stimulus or to have no effect on meaning (i.e., to influence conceptual processing or not). Abstract visual shapes (squiggles) were colorized during study and presented during test in either the same color or a different color. Those squiggles that subjects found to resemble meaningful objects supported behavioral measures of conceptual priming, whereas meaningless squiggles did not. Further, changing color from study to test had a selective effect on behavioral correlates of priming for meaningful squiggles, indicating that color change altered conceptual processing. During a recognition memory test, color change altered event-related brain potential correlates of memory for meaningful squiggles but not for meaningless squiggles. Specifically, color change reduced the amplitude of frontally distributed N400 potentials (FN400), indicating that these potentials indicated conceptual processing during recognition memory that was sensitive to color change. In contrast, color change had no effect on FN400 correlates of recognition for meaningless squiggles, which were overall smaller in amplitude than for meaningful squiggles (further indicating that these potentials signal conceptual processing during recognition). Thus, merely changing the color of abstract visual shapes can alter their meaning, changing behavioral and neural correlates of memory

Temporal expectation improves recognition memory for spatially attended objects

Recent evidence suggests that temporal expectation is beneficial to memory formation. Rhythmic presentation of stimuli during encoding enhances subsequent recognition and is associated with distinct neural activity compared with when stimuli are presented in an arrhythmic manner. However, no prior study has examined how temporal expectation interacts with another important form of facilitation – spatial attention – to affect memory. This study systematically manipulated temporal expectation and spatial attention during encoding to examine their combined effect on behavioural recognition and associated ERPs. Participants performed eight experimental blocks consisting of an encoding phase and recognition test, with EEG recorded throughout. During encoding, pairs of objects and checkerboards were presented and participants were cued to attend to the left or right stream and detect targets as quickly as possible. In four blocks stimulus presentation followed a rhythmic (constant, predictable) temporal structure, and in the other four blocks stimulus onset was arrhythmic (random, unpredictable). An interaction between temporal expectation and spatial attention emerged, with greater recognition in the rhythmic than the arrhythmic condition for spatially attended items. Analysis of memory specific ERP components uncovered effects of spatial attention. There were late positive component (LPC) and FN400 old/new effects in the attended condition for both rhythmic and arrhythmic items, while in the unattended condition there was an FN400 old/new effect, and no LPC effect. The study provides new evidence that memory improvement as a function of temporal expectation is dependent upon spatial attention

Is faster better? Effects of response deadline on ERP correlates of recognition memory in younger and older adults

Aging studies generally suggest that recollection is impaired whereas familiarity-based recognition remains relatively preserved in healthy older adults. The present event-related potential (ERP) study explores whether age-related impairments in recognition memory can be reduced under conditions in which recognition decisions are primarily driven by familiarity. Old and young adults performed an item recognition task with perceptually rich visual stimuli. A response deadline procedure was employed following previous studies which have shown that limiting response times attenuates recollection but leaves familiarity relatively unaffected. Age effects on memory performance were large in the non-speeded response condition in which recollection contributes to performance. When response time was limited, performance differences between groups were negligible. In the non-speeded condition the ERP correlate of recollection was not detectable in old adults. Conversely, in the speeded condition ERP correlates of familiarity were obtained in both age groups, though attenuated for old adults. For old adults in the speeded condition a temporally extended posterior negativity was obtained which was more pronounced for low performing participants. The results suggest that even though the neural generators of the familiarity signal degrade with age, familiarity is an important contributor to recognition memory in older adults and can lead to a disproportional benefit in memory in conditions designed to specifically enhance familiarity-based responding

Rhythmic temporal structure at encoding enhances recognition memory

Presenting events in a rhythm has been shown to enhance perception and facilitate responses for stimuli that appear in synchrony with the rhythm, but little is known about how rhythm during encoding influences later recognition. In this study, participants were presented with images of everyday objects in an encoding phase prior to a recognition task in which they judged whether or not objects were previously presented. Blockwise, object presentation during encoding followed either a rhythmic (constant, predictable) or arrhythmic (random, unpredictable) temporal structure, of which participants were unaware. Recognition was greater for items presented in a rhythmic relative to an arrhythmic manner. During encoding, there was a Dm effect with larger positivity for rhythmic over arrhythmic stimuli. At recognition, memory specific ERP components were differentially affected by temporal structure: the FN400 old/new effect was unaffected by rhythmic structure, whilst the late positive component (LPC) old/new effect was observed only for rhythmically encoded items. Taken together, this study provides new evidence that memory specific processing at recognition is affected by temporal structure at encoding

The effect of aging and rhythmic temporal structure during encoding on recognition memory: an EEG Study

Aging deficits in memory have long been established in the literature, however, little has been done to investigate how environmental factors can be used to ameliorate age related declines in memory functioning. Recent research in recognition memory suggests that increased temporal expectancy during encoding can benefit recognition memory at retrieval in a younger adult sample. The current study aimed to investigate whether the benefit to recognition memory, and associated neural processes, observed in young adults is also evident in normal aging. Unfortunately, due to national restrictions affecting data collection, no older participants were able to be tested. As such, the current project resolved to provide a proof of concept to inform an investigation of the originally intended scope. Ten young participants (M age = 23.5; SD = 2.22) were exposed to pictures of everyday objects in 3 rhythmic and 3 arrhythmic encoding blocks, after which they performed a recognition memory test containing previously studied and new objects. A clear trend suggesting better memory following rhythmic encoding was observed, but no significant difference between conditions emerged. Furthermore, analysis of relevant ERP components uncovered no old/new effect in relation to the LPC or the LFE. Conversely, the FN400 displayed an old/new effect. Thus, the temporal manipulation did not result in significant differences in recognition, but it should be noted that the study is underpowered. However, participants did display a good ability to discriminate stimuli, and in addition RT differences between correct and incorrect recognition judgements and an FN400 old/new effect suggest that the paradigm is effective and sensitive to processing differences between conditions. Recognition could be detected by the FN400 in the present experiment. However, trends in recognition ability between temporal structures suggest that an insufficient sample size is likely to have caused the lacking significant temporal effects. As such, the paradigm is appropriate for extension including a larger sample size and the planned comparison of age groups

Rhythmic temporal structure at encoding enhances recognition memory

Presenting events in a rhythm has been shown to enhance perception and facilitate responses for stimuli that appear in synchrony with the rhythm, but little is known about how rhythm during encoding influences later recognition. In this study, participants were presented with images of everyday objects in an encoding phase prior to a recognition task in which they judged whether or not objects were previously presented. Blockwise, object presentation during encoding followed either a rhythmic (constant, predictable) or arrhythmic (random, unpredictable) temporal structure, of which participants were unaware. Recognition was greater for items presented in a rhythmic relative to an arrhythmic manner. During encoding, there was a Dm effect with larger positivity for rhythmic over arrhythmic stimuli. At recognition, memory specific ERP components were differentially affected by temporal structure: the FN400 old/new effect was unaffected by rhythmic structure, whilst the late positive component (LPC) old/new effect was observed only for rhythmically encoded items. Taken together, this study provides new evidence that memory specific processing at recognition is affected by temporal structure at encoding

Exploring the Nature of Neural Correlates of Language, Attention and Memory: Reliability and Validity Studies of Event Related Potentials

Comparing data from different subfields of research may help in understanding emerging patterns and refining interpretations. This is especially true in neuroscience because brain functions can be studied at multiple levels of analysis, spatially and temporally, and with a variety of complementary measurement techniques. Within the ERP domain, several subfields of research have evolved over time, typically reflecting the specific time-window of interest and brain function investigated. The current investigation focused on three widely studied ERP effects reflecting a variety of key brain functions: the N400 effect, the P3b effect and the Left Parietal effect. The N400 effect has attracted researchers interested in language processing, the P3b effect researchers interested in attentional processes and the Left Parietal effect researchers focused on episodic recollection. Even though the ERP technology constitutes a common thread across these subfields, there is often a lack of communication across groups of researchers. The literatures on the N400 effect, P3b effect and Left Parietal effect have been written by relatively non-overlapping groups of researchers, and as such the kind of analysis carried out in the current thesis is not a common one, as it compares effects investigated within different subfields. Specifically, the approach taken in the current thesis involves assessment of the comparative reliability of the three effects of interest, and at the same time allowing refining their validity. Results showed that all three effects were found to be reliable at the group level and the N400 effect and the P3b effect were also found to be reliable at the single participant level. A correlational analysis involving all three effects yielded a significant correlation between the P3b and the Left Parietal effect but not between the P3b and the N400, or between the Left Parietal effect and the N400. Following up on the significant correlation, suggesting a convergence between the P3b effect and the Left Parietal effect, a probability manipulation of the Left Parietal effect was carried out to investigate if the old/new effect is sensitive to probability changes similarly to the P3b. The size of the Left Parietal effect was found to be sensitive to the relative probability of old and new items, in a manner consistent with the P3b effect‟s sensitivity to probability manipulations. The results pointing to a relationship between the P3b effect and the Left Parietal effect suggest that attentional processes sensitive to probability may temporally overlap and confound memory processes as indexed by the Left Parietal effect. The N400 effect, in the initial correlational study, was found to be independent from attentional processes as reflected by the P3b, and from episodic recollection as indexed by the Left Parietal effect. The validity of the N400 effect as a measure of semantic processing was then assessed by manipulating associative relationships while keeping constant semantic relationships, with results showing that the effect can be clearly modulated by associative changes when semantic relatedness is kept constant. The same association norms were then used in an old/new recognition experiment to assess if the Bilateral-Frontal old/new effect behaves in reaction to association relationships similarly or differently from the N400, in the attempt of assessing if the N400 is only a measure of associative relationships or also a measure of the process of familiarity. The observed pattern suggests independence between the N400 and the Bilateral Frontal effect. Overall, the N400 effect was found to be independent from memory processes occurring in the same time window, but, contrary to the dominant interpretation of the effect, the effect was modulated by changes in association strength while keeping semantic relatedness constant, suggesting that the N400 effect may be sensitive to a contiguity-based associative learning process not constrained to the linguistic domain

On the mnemonic benefits of drawing

Researchers have long sought to explore means through which the amount, and quality of information one is able to remember can be improved. Attention has been paid variously to multimodal encoding, visual learning, and deep elaborative processing of to-be-remembered information in pursuit of this goal. Drawing is a relatively easily implemented task that engages many of the foregoing, and therefore is an excellent candidate task for systematic exploration. In this dissertation, the efficacy of drawing is explored as a potentially potent, memory-bolstering encoding strategy, and possible explanatory mechanisms are explored. In Chapter II, drawing at encoding is compared to writing, and leads to better free recall. Drawing is also contrasted with other tasks, indicating that the benefit cannot be fully explained by elaborative encoding, visual imagery, or picture superiority. Drawing led to a large boost in free recall in both within- and between-subjects designs, thereby ruling out within-list distinctiveness as a comprehensive explanatory mechanism. In Chapter III, drawing and writing are again compared, this time using recognition task variants, revealing that the memory benefits of drawing are driven primarily by detailed, recollection-based memory. A component model of the benefit drawing provides to memory is proposed, which holds that the effect of drawing is driven by the confluence of three beneficial components required in drawing – an elaborative component, to derive an internal concept of what to draw based on a target word; a motor component, to translate that internal image to the page using a specific manual motor program; and a pictorial component, derived from one’s newly created depiction of the original target word. In Chapter IV, this component model is tested using tasks which systematically do or do not require each of the requisite components of the drawing process. Results indicate that each component is an important contributor to the benefit, and that memory performance scales up as the number of components increases. Taken together, the experiments presented herein indicate that drawing is a potent encoding task which improves memory through the provision, and integration of rich contextual information from at least three multisensory components