The Experts below are selected from a list of 32334 Experts worldwide ranked by ideXlab platform
John T. Wixted - One of the best experts on this subject based on the ideXlab platform.
-
Psychophysical scaling reveals a unified theory of visual Memory Strength
Nature Human Behaviour, 2020Co-Authors: Mark W. Schurgin, John T. Wixted, Timothy F. BradyAbstract:Schurgin et al. propose a model of visual Memory, arguing against a distinction between how many items are represented and how precisely they are represented, and in favour of a view based on continuous representations in noisy channels. Almost all models of visual Memory implicitly assume that errors in mnemonic representations are linearly related to distance in stimulus space. Here we show that neither Memory nor perception are appropriately scaled in stimulus space; instead, they are based on a transformed similarity representation that is nonlinearly related to stimulus space. This result calls into question a foundational assumption of extant models of visual working Memory. Once psychophysical similarity is taken into account, aspects of Memory that have been thought to demonstrate a fixed working Memory capacity of around three or four items and to require fundamentally different representations—across different stimuli, tasks and types of Memory—can be parsimoniously explained with a unitary signal detection framework. These results have substantial implications for the study of visual Memory and lead to a substantial reinterpretation of the relationship between perception, working Memory and long-term Memory.
-
psychophysical scaling reveals a unified theory of visual Memory Strength
bioRxiv, 2018Co-Authors: Mark W. Schurgin, John T. Wixted, Timothy F. BradyAbstract:Abstract Models of visual Memory have operated on the assumption that Memory representations can be explained in physical stimulus space, leading to proposals that we have fixed limits on visual working Memory capacity and there is a strong distinction between working Memory and longterm Memory representations. Here we show that perception and Memory are not based on physical stimulus space, and instead rely on a transformed representation that is non-linearly related to the physical stimulus space. This result calls into question the fundamental basis of nearly all extant models. We show that when psychophysical distance rather than physical distance is considered, aspects of Memory that have required fundamentally different models -- across different stimuli, tasks, and even the distinction between working and long-term Memory -- can be explained with a unitary signal detection framework. These results lead to a substantial reinterpretation of the relationship between perception, working Memory and longterm Memory.
-
different nonlinear functions in hippocampus and perirhinal cortex relating functional mri activity to Memory Strength
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Zhuang Song, John T. Wixted, Christine N Smith, Larry R SquireAbstract:Findings from functional MRI (fMRI) studies of recognition Memory and the medial temporal lobe often suggest qualitative differences in the contribution of the hippocampus and perirhinal cortex. This interpretation is complicated by the fact that most of the methods intended to demonstrate qualitative differences also separate strong memories from weak memories. Thus, apparent qualitative differences might reflect quantitative differences in how measured activity in medial temporal lobe structures varies with Memory Strength. We tested the hypothesis that the relationship between activity at the time of study and subsequent Memory Strength is nonlinear in hippocampus and perirhinal cortex and also distinctly different in those two structures. We found that activity in the hippocampus was characterized by a positively accelerated function and that activity in the perirhinal cortex was associated with a statistically different, negatively accelerated function. Our results do not count against the possibility that these structures differ qualitatively in their contributions to Memory. Rather, our findings show how an alternative interpretation based on quantitative differences can also account for a good deal of data, and they suggest that a demonstration of qualitative differences requires more stringent criteria than are achieved in most fMRI studies.
-
Recollection Is a Continuous Process Implications for Dual-Process Theories of Recognition Memory
Psychological Science, 2009Co-Authors: Laura Mickes, Peter E Wais, John T. WixtedAbstract:Dual-process theory, which holds that recognition decisions can be based on recollection or familiarity, has long seemed incompatible with signal detection theory, which holds that recognition decisions are based on a singular, continuous Memory-Strength variable. Formal dual-process models typically regard familiarity as a continuous process (i.e., familiarity comes in degrees), but they construe recollection as a categorical process (i.e., recollection either occurs or does not occur). A continuous process is characterized by a graded relationship between confidence and accuracy, whereas a categorical process is characterized by a binary relationship such that high confidence is associated with high accuracy but all lower degrees of confidence are associated with chance accuracy. Using a source-Memory procedure, we found that the relationship between confidence and source-recollection accuracy was graded. Because recollection, like familiarity, is a continuous process, dual-process theory is more compat...
-
activity in the medial temporal lobe predicts Memory Strength whereas activity in the prefrontal cortex predicts recollection
The Journal of Neuroscience, 2008Co-Authors: Brock C Kirwan, John T. Wixted, Larry R SquireAbstract:Functional magnetic resonance imaging studies of recognition Memory have often been interpreted to mean that the hippocampus supports recollection and that the adjacent perirhinal cortex supports familiarity. Other work points out that these studies have confounded recollection and familiarity with strong and weak memories. In a source Memory study, we used two novel approaches to data analysis that allowed item Memory Strength and source Memory Strength to be assessed independently. First, we identified regions in both hippocampus and perirhinal cortex in which activity varied as a function of subsequent item Memory Strength while source Memory Strength was held constant at chance levels. Second, we identified regions in prefrontal cortex in which activity varied as a function of subsequent source Memory Strength while item Memory Strength was held constant. These findings suggest that activity in the medial temporal lobe is predictive of subsequent Memory Strength, whereas activity in prefrontal cortex is predictive of subsequent recollection.
Anthony D Wagner - One of the best experts on this subject based on the ideXlab platform.
-
functional heterogeneity in posterior parietal cortex across attention and episodic Memory retrieval
Cerebral Cortex, 2014Co-Authors: Benjamin J Hutchinson, Alison R Preston, Melina R Uncapher, Kevin S Weiner, David W Bressler, Michael A Silver, Anthony D WagnerAbstract:While attention is critical for event Memory, debate has arisen regarding the extent to which posterior parietal cortex (PPC) activation during episodic retrieval reflects engagement of PPC-mediated mechanisms of attention. Here, we directly examined the relationship between attention and Memory, within and across subjects, using functional magnetic resonance imaging attention-mapping and episodic retrieval paradigms. During retrieval, 4 functionally dissociable PPC regions were identified. Specifically, 2 PPC regions positively tracked retrieval outcomes: lateral intraparietal sulcus (latIPS) indexed graded item Memory Strength, whereas angular gyrus (AnG) tracked recollection. By contrast, 2 other PPC regions demonstrated nonmonotonic relationships with retrieval: superior parietal lobule (SPL) tracked retrieval reaction time, consistent with a graded engagement of top-down attention, whereas temporoparietal junction displayed a complex pattern of below-baseline retrieval activity, perhaps reflecting disengagement of bottom-up attention. Analyses of retrieval effects in PPC topographic spatial attention maps (IPS0-IPS5; SPL1) revealed that IPS5 and SPL1 exhibited a nonmonotonic relationship with retrieval outcomes resembling that in the SPL region, further suggesting that SPL activation during retrieval reflects top-down attention. While demands on PPC attention mechanisms vary during retrieval attempts, the present functional parcellation of PPC indicates that 2 additional mechanisms (mediated by latIPS and AnG) positively track retrieval outcomes.
-
high resolution fmri of content sensitive subsequent Memory responses in human medial temporal lobe
Journal of Cognitive Neuroscience, 2010Co-Authors: Alison R Preston, Benjamin J Hutchinson, Aaron M Bornstein, Meghan E Gaare, Gary H Glover, Anthony D WagnerAbstract:The essential role of the medial temporal lobe (MTL) in long-term Memory for individual events is well established, yet important questions remain regarding the mnemonic functions of the component structures that constitute the region. Within the hippocampus, recent functional neuroimaging findings suggest that formation of new memories depends on the dentate gyrus and the CA3 field, whereas the contribution of the subiculum may be limited to retrieval. During encoding, it has been further hypothesized that structures within MTL cortex contribute to encoding in a content-sensitive manner, whereas hippocampal structures may contribute to encoding in a more domain-general manner. In the current experiment, high-resolution fMRI techniques were utilized to assess novelty and subsequent Memory effects in MTL subregions for two classes of stimuli-faces and scenes. During scanning, participants performed an incidental encoding (target detection) task with novel and repeated faces and scenes. Subsequent recognition Memory was indexed for the novel stimuli encountered during scanning. Analyses revealed voxels sensitive to both novel faces and novel scenes in all MTL regions. However, similar percentages of voxels were sensitive to novel faces and scenes in perirhinal cortex, entorhinal cortex, and a combined region comprising the dentate gyrus, CA2, and CA3, whereas parahippocampal cortex, CA1, and subiculum demonstrated greater sensitivity to novel scene stimuli. Paralleling these findings, subsequent Memory effects in perirhinal cortex were observed for both faces and scenes, with the magnitude of encoding activation being related to later Memory Strength, as indexed by a graded response tracking recognition confidence, whereas subsequent Memory effects were scene-selective in parahippocampal cortex. Within the hippocampus, encoding activation in the subiculum correlated with subsequent Memory for both stimulus classes, with the magnitude of encoding activation varying in a graded manner with later Memory Strength. Collectively, these findings suggest a gradient of content sensitivity from posterior (parahippocampal) to anterior (perirhinal) MTL cortex, with MTL cortical regions differentially contributing to successful encoding based on event content. In contrast to recent suggestions, the present data further indicate that the subiculum may contribute to successful encoding irrespective of event content.
-
Memory Strength and repetition suppression multimodal imaging of medial temporal cortical contributions to recognition
Neuron, 2005Co-Authors: Brian D Gonsalves, Itamar Kahn, Tim Curran, Kenneth A Norman, Anthony D WagnerAbstract:Declarative Memory permits an organism to recognize stimuli that have been previously encountered, discriminating them from those that are novel. One basis for recognition is item Memory Strength, which may support the perception of stimulus familiarity. Though the medial temporal lobes are known to be critical for declarative Memory, at present the neural mechanisms supporting perceived differences in Memory Strength remain poorly specified. Here, functional MRI (fMRI) and anatomically constrained magnetoencephalography (MEG) indexed correlates of graded Memory Strength in the human brain, focusing on medial temporal cortex. fMRI revealed a decrease in medial temporal cortical activation that tracked parametric levels of perceived Memory Strength. Anatomically constrained MEG current estimates revealed that Strength-dependent signal reductions onset within 150-300 ms. Memory Strength appears to be rapidly signaled by medial temporal cortex through repetition suppression (activation reductions), providing a basis for the subjective perception of stimulus familiarity or novelty.
Peter E Wais - One of the best experts on this subject based on the ideXlab platform.
-
Recollection Is a Continuous Process Implications for Dual-Process Theories of Recognition Memory
Psychological Science, 2009Co-Authors: Laura Mickes, Peter E Wais, John T. WixtedAbstract:Dual-process theory, which holds that recognition decisions can be based on recollection or familiarity, has long seemed incompatible with signal detection theory, which holds that recognition decisions are based on a singular, continuous Memory-Strength variable. Formal dual-process models typically regard familiarity as a continuous process (i.e., familiarity comes in degrees), but they construe recollection as a categorical process (i.e., recollection either occurs or does not occur). A continuous process is characterized by a graded relationship between confidence and accuracy, whereas a categorical process is characterized by a binary relationship such that high confidence is associated with high accuracy but all lower degrees of confidence are associated with chance accuracy. Using a source-Memory procedure, we found that the relationship between confidence and source-recollection accuracy was graded. Because recollection, like familiarity, is a continuous process, dual-process theory is more compat...
-
fmri signals associated with Memory Strength in the medial temporal lobes a meta analysis
Neuropsychologia, 2008Co-Authors: Peter E WaisAbstract:To identify patterns of Memory-related neural activity in the medial temporal lobes (MTL), a quantitative meta-analysis of 17 functional magnetic resonance imaging (fMRI) studies was performed. The analysis shows that increased activity in the hippocampus and the parahippocampal cortex predicts subsequent Memory Strength. During retrieval, activity in the hippocampus increases in association with strong Memory. In the perirhinal cortex, increased activity predicts subsequent recognition, whether based on weak or strong Memory, whereas during retrieval activity decreases below the level for misses in association with both weak and strong Memory. The results are consistent with the claim that the hippocampus selectively subserves recollection, whereas adjacent structures subserve familiarity [Eichenbaum, H., Yonelinas, A., & Ranganath, C. (2007). The medial temporal lobe and recognition Memory. The Annual Review of Neuroscience, 30, 123-152]. However, this conclusion depends on a specific dual-process theory of recognition Memory that has been used to interpret the results. An alternative dual-process model holds that the behavioral methods used to differentiate recollection from familiarity instead separate strong memories from weak memories. When the fMRI data are interpreted in terms of the alternative theory, the fMRI results do not point to selective roles for the hippocampus or the adjacent MTL structures. The fMRI data alone cannot distinguish between these two models, so other methods are needed to resolve the issue.
-
a direct test of the unequal variance signal detection model of recognition Memory
Psychonomic Bulletin & Review, 2007Co-Authors: Laura Mickes, John T. Wixted, Peter E WaisAbstract:Analyses of the receiver operating characteristic (ROC) almost invariably suggest that, on a recognition Memory test, the standard deviation of Memory Strengths associated with the lures (σlure) is smaller than that of the targets (σtarget). Often, σlure/σtarget ≈ 0.80. However, that conclusion is based on a model that assumes that the Memory Strength distributions are Gaussian in form. In two experiments, we investigated this issue in a more direct way by asking subjects to simply rate the Memory Strengths of targets and lures using a 20-point or a 99-point Strength scale. The results showed that the standard deviation of the ratings made to the targets (starget) was, indeed, larger than the standard deviation of the ratings made to the lures (slure). Moreover, across subjects, the ratioslure/starget correlated highly with the estimate of σlure/σtarget obtained from ROC analysis, and both estimates were, on average, approximately equal to 0.80.
-
the hippocampus supports both the recollection and the familiarity components of recognition Memory
Neuron, 2006Co-Authors: Peter E Wais, John T. Wixted, Ramona O Hopkins, Larry R SquireAbstract:The receiver operating characteristic (ROC) has been used to investigate the component processes of recognition Memory. Some studies with this technique have been taken to indicate that the hippocampus selectively supports the process of recollection, whereas adjacent cortex in the parahippocampal gyrus supports the process of familiarity. We analyzed ROC data from young adults, Memory-impaired patients with limited hippocampal lesions, and age-matched controls. The shape of the ROC changed in similar ways from asymmetric to symmetric, as a function of the Strength of Memory (strong to weak) in both the young adults and the patients. Moreover, once overall Memory Strength was similar, the shape of the patient ROC was asymmetric and matched the control ROC. These results suggest that the component processes that determine the shape of the ROC are operative in the absence of the hippocampus, and they argue against the idea that the hippocampus selectively supports the recollection process.
Larry R Squire - One of the best experts on this subject based on the ideXlab platform.
-
medial temporal lobe function and recognition Memory a novel approach to separating the contribution of recollection and familiarity
The Journal of Neuroscience, 2011Co-Authors: Zhuang Song, Annette Jeneson, Larry R SquireAbstract:Human neuroimaging studies of recognition Memory have often been interpreted to mean that the hippocampus supports recollection but not familiarity. This interpretation is complicated by the fact that recollection-based decisions are typically associated with stronger memories than familiarity-based decisions. Some studies of source Memory controlled for this difference in Memory Strength and found that hippocampal activity during learning predicted subsequent item Memory Strength while recollection-based Memory (performance on source Memory questions) was held at chance. This result suggests that the hippocampus is important for familiarity. However, a difficulty with this approach is that when source Memory is assessed by asking specific, task-relevant source Memory questions, participants who fail to answer the prescribed questions might nevertheless have available other (task-irrelevant) source information. Accordingly, successful item Memory could still be associated with recollection. The present study used a novel method to assess item Memory and source Memory. Instead of responding to specific source questions, participants rated their source Memory Strength based on any information about the learning episode that was available to them. When subsequent source Memory Strength was held constant at the lowest possible level, we identified regions bilaterally in hippocampus, as well as in perirhinal cortex, where activity during learning increased as subsequent item Memory increased in Strength. In addition, activity in cortical regions (including prefrontal cortex) was related to source Memory success independently of item Memory Strength. These findings suggest that activity in the hippocampus is related to the encoding of familiarity-based item Memory, independent of subsequent recollection-based success.
-
different nonlinear functions in hippocampus and perirhinal cortex relating functional mri activity to Memory Strength
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Zhuang Song, John T. Wixted, Christine N Smith, Larry R SquireAbstract:Findings from functional MRI (fMRI) studies of recognition Memory and the medial temporal lobe often suggest qualitative differences in the contribution of the hippocampus and perirhinal cortex. This interpretation is complicated by the fact that most of the methods intended to demonstrate qualitative differences also separate strong memories from weak memories. Thus, apparent qualitative differences might reflect quantitative differences in how measured activity in medial temporal lobe structures varies with Memory Strength. We tested the hypothesis that the relationship between activity at the time of study and subsequent Memory Strength is nonlinear in hippocampus and perirhinal cortex and also distinctly different in those two structures. We found that activity in the hippocampus was characterized by a positively accelerated function and that activity in the perirhinal cortex was associated with a statistically different, negatively accelerated function. Our results do not count against the possibility that these structures differ qualitatively in their contributions to Memory. Rather, our findings show how an alternative interpretation based on quantitative differences can also account for a good deal of data, and they suggest that a demonstration of qualitative differences requires more stringent criteria than are achieved in most fMRI studies.
-
activity in the medial temporal lobe predicts Memory Strength whereas activity in the prefrontal cortex predicts recollection
The Journal of Neuroscience, 2008Co-Authors: Brock C Kirwan, John T. Wixted, Larry R SquireAbstract:Functional magnetic resonance imaging studies of recognition Memory have often been interpreted to mean that the hippocampus supports recollection and that the adjacent perirhinal cortex supports familiarity. Other work points out that these studies have confounded recollection and familiarity with strong and weak memories. In a source Memory study, we used two novel approaches to data analysis that allowed item Memory Strength and source Memory Strength to be assessed independently. First, we identified regions in both hippocampus and perirhinal cortex in which activity varied as a function of subsequent item Memory Strength while source Memory Strength was held constant at chance levels. Second, we identified regions in prefrontal cortex in which activity varied as a function of subsequent source Memory Strength while item Memory Strength was held constant. These findings suggest that activity in the medial temporal lobe is predictive of subsequent Memory Strength, whereas activity in prefrontal cortex is predictive of subsequent recollection.
-
activity in both hippocampus and perirhinal cortex predicts the Memory Strength of subsequently remembered information
Neuron, 2008Co-Authors: Yael Shrager, Brock C Kirwan, Larry R SquireAbstract:Summary It has been suggested that hippocampal activity predicts subsequent recognition success when recognition decisions are based disproportionately on recollection, whereas perirhinal activity predicts recognition success when decisions are based primarily on familiarity. Another perspective is that both hippocampal and perirhinal activity are predictive of overall Memory Strength. We tested the relationship between brain activity during learning and subsequent Memory Strength. Activity in a number of cortical regions (including regions within the "default network") was negatively correlated with subsequent Memory Strength, suggesting that this activity reflects inattention or mind wandering (and, consequently, poor Memory). In contrast, activity in both hippocampus and perirhinal cortex positively correlated with the subsequent Memory Strength of remembered items. This finding suggests that both structures cooperate during learning to determine the Memory Strength of what is being learned.
-
the hippocampus supports both the recollection and the familiarity components of recognition Memory
Neuron, 2006Co-Authors: Peter E Wais, John T. Wixted, Ramona O Hopkins, Larry R SquireAbstract:The receiver operating characteristic (ROC) has been used to investigate the component processes of recognition Memory. Some studies with this technique have been taken to indicate that the hippocampus selectively supports the process of recollection, whereas adjacent cortex in the parahippocampal gyrus supports the process of familiarity. We analyzed ROC data from young adults, Memory-impaired patients with limited hippocampal lesions, and age-matched controls. The shape of the ROC changed in similar ways from asymmetric to symmetric, as a function of the Strength of Memory (strong to weak) in both the young adults and the patients. Moreover, once overall Memory Strength was similar, the shape of the patient ROC was asymmetric and matched the control ROC. These results suggest that the component processes that determine the shape of the ROC are operative in the absence of the hippocampus, and they argue against the idea that the hippocampus selectively supports the recollection process.
Ueli Rutishauser - One of the best experts on this subject based on the ideXlab platform.
-
single neuron representation of Memory Strength and recognition confidence in left human posterior parietal cortex
Neuron, 2018Co-Authors: Ueli Rutishauser, Tyson Aflalo, Emily R Rosario, Nader Pouratian, Richard A AndersenAbstract:The human posterior parietal cortex (PPC) is thought to contribute to Memory retrieval, but little is known about its specific role. We recorded single PPC neurons of two human tetraplegic subjects implanted with microelectrode arrays, who performed a recognition Memory task. We found two groups of neurons that signaled Memory-based choices. Memory-selective neurons preferred either novel or familiar stimuli, scaled their response as a function of confidence, and signaled subjective choices regardless of truth. Confidence-selective neurons signaled confidence regardless of stimulus familiarity. Memory-selective signals appeared 553 ms after stimulus onset, but before action onset. Neurons also encoded spoken numbers, but these number-tuned neurons did not carry recognition signals. Together, this functional separation reveals action-independent coding of declarative Memory-based familiarity and confidence of choices in human PPC. These data suggest that, in addition to sensory-motor integration, a function of human PPC is to utilize Memory signals to make choices.
-
persistently active neurons in human medial frontal and medial temporal lobe support working Memory
Nature Neuroscience, 2017Co-Authors: Jan Kaminski, Shannon Sullivan, Jeffrey M Chung, Ian B Ross, Adam N Mamelak, Ueli RutishauserAbstract:Persistent neural activity is a putative mechanism for the maintenance of working memories. Persistent activity relies on the activity of a distributed network of areas, but the differential contribution of each area remains unclear. We recorded single neurons in the human medial frontal cortex and medial temporal lobe while subjects held up to three items in Memory. We found persistently active neurons in both areas. Persistent activity of hippocampal and amygdala neurons was stimulus-specific, formed stable attractors and was predictive of Memory content. Medial frontal cortex persistent activity, on the other hand, was modulated by Memory load and task set but was not stimulus-specific. Trial-by-trial variability in persistent activity in both areas was related to Memory Strength, because it predicted the speed and accuracy by which stimuli were remembered. This work reveals, in humans, direct evidence for a distributed network of persistently active neurons supporting working Memory maintenance.
-
representation of retrieval confidence by single neurons in the human medial temporal lobe
Nature Neuroscience, 2015Co-Authors: Ueli Rutishauser, Jeffrey M Chung, Ian B Ross, Matthieu Koroma, Oana Tudusciuc, Adam N MamelakAbstract:Memory-based decisions are often accompanied by an assessment of choice certainty, but the mechanisms of such confidence judgments remain unknown. We studied the response of 1,065 individual neurons in the human hippocampus and amygdala while neurosurgical patients made Memory retrieval decisions together with a confidence judgment. Combining behavioral, neuronal and computational analysis, we identified a population of Memory-selective (MS) neurons whose activity signaled stimulus familiarity and confidence, as assessed by subjective report. In contrast, the activity of visually selective (VS) neurons was not sensitive to Memory Strength. The groups further differed in response latency, tuning and extracellular waveforms. The information provided by MS neurons was sufficient for a race model to decide stimulus familiarity and retrieval confidence. Together, our results indicate a trial-by-trial relationship between a specific group of neurons and declared Memory Strength in humans. We suggest that VS and MS neurons are a substrate for declarative memories.
-
human Memory Strength is predicted by theta frequency phase locking of single neurons
Nature, 2010Co-Authors: Ueli Rutishauser, Ian B Ross, Adam N Mamelak, Erin M SchumanAbstract:Learning from novel experiences is a major task of the central nervous system. In mammals, the medial temporal lobe is crucial for this rapid form of learning. The modification of synapses and neuronal circuits through plasticity is thought to underlie Memory formation. The induction of synaptic plasticity is favoured by coordinated action-potential timing across populations of neurons. Such coordinated activity of neural populations can give rise to oscillations of different frequencies, recorded in local field potentials. Brain oscillations in the theta frequency range (3–8 Hz) are often associated with the favourable induction of synaptic plasticity as well as behavioural Memory. Here we report the activity of single neurons recorded together with the local field potential in humans engaged in a learning task. We show that successful Memory formation in humans is predicted by a tight coordination of spike timing with the local theta oscillation. More stereotyped spiking predicts better Memory, as indicated by higher retrieval confidence reported by subjects. These findings provide a link between the known modulation of theta oscillations by many Memory-modulating behaviours and circuit mechanisms of plasticity.