The Neural correlates of conceptual and perceptual false recognition

Rachel J. Garoff-Eaton, Elizabeth A. Kensinger and Daniel L. Schacter

Learning & Memory 14:684-692 (2007)

False recognition, broadly defined as a claim to remember something that was not encountered previously, can arise for multiple reasons. Foe instance, a distinction can be made between conceptual false recognition (i.e., false alarms resulting from semantic or associative similarities between studied and tested items) and perceptual false recognition (i.e., false alarms resulting from physical similarities between studied and tested items). Although false recognition has been associated with frontal cortex activity, it is unclear whether this frontal activity can be modulated by the precise relationship between studied and falsely remembered items. We used event-related fMRI to examine the neural basis of conceptual compared with perceptual false recognition. Results revealed preferential activity in multiple frontal cortex regions during conceptual false recognition, which likely reflected increased semantic processing during conceptual (but not perceptual) memory errors. These results extend recent reports that different types of false recognition can rely on dissociable neural substrates, and they indicate that the frontal activity that is often observed during false compared with true recognition can be modulated by the relationship between studied and tested items.

Age-related changes in cognitive conflict processing: An event-related potential study

Ralph Mager, Alex H. Bullinger, Serge Brand, Maria Schmidlin, Heinz Sch¨arli, Franz M¨uller-Spahn, Robert St¨ormer, Michael Falkenstein

Neurobiology of Aging 28:1925-1935 (2007)

Cognitive tasks involving conflicting stimuli and responses are associated with an early age-related decline in performance. Conflict and conflict-induced interference can be stimulus- or response-related. In classical stimulus-response compatibility tasks, such as the Stroop task, the event-related potential (ERP) usually reveals a greater negativity on incongruent versus congruent trials which has often been linked with conflict processing. However, it is unclear whether this negativity is related stimulus- or response-related conflict, thus rendering the meaning of age-related changes inconclusive. In the present study, a modified Stroop task was used to focus on stimulus-related interference processes while excluding response-related interference. Since we intended to study work-relevant effects ERP and performance were determined in young (about 30 years old) and middle-aged (about 50 years old) healthy subjects (total n=80). In the ERP, a broad negativity developed after incongruent versus congruent stimuli between 350ms and 650ms. An age-related increase of the latency and amplitude of this negativity was observed. These results indicate age-related alterations in the processing of conflicting stimuli already in middle age.

Common and distinct neural substrates of attentional control in an integrated Simon and spatial Stroop task as assessed by event-related fMRI

Xun Liu, Marie T. Banich, Benjamin L. Jacobson, and Jody L. Tanabe

NeuroImage 22: 1097-1106 (2004)

The purpose of this experiment was to directly examine the neural mechanism of attentional control involved in the Simon task as compared to a spatial Stroop task using event-related fMRI. The Simon effect typically refers to the interference people experience when there is a stimulus-response conflict. The Stroop effect refers to the interference people experience when two attributes of the same stimulus conflict with each other. Although previous imaging studies have compared the brain activation for each of these tasks performed separately, none had done so in an integrated task that incorporates both types of interference, as was done in the current experiment. Both tasks activated brain regions that serve as a source of attentional control (dorsolateral prefrontal cortex) and posterior regions that are sites of attentional control (the visual processing stream-middle occipital and inferior temporal cortices). In addition, there were also specific brain regions activated to a significantly greater degree by one task and/or only by a single task. The brain regions significantly more activated by the Simon task were those sensitive to detection of response conflict, response selection, and planning (anterior cingulated cortex, supplementary motor areas, and precuneus), and visuospatial motor association areas. In contrast, the region significantly more activated by the Stroop task were those involved in biasing the processing toward the task-relevant attribute (inferior parietal cortex). These findings suggest that the interference effects of these two tasks are caused by different types of conflict (stimulus-response conflict for the Simon effect and stimulus-stimulus conflict for the Stroop effect) but both invoke similar sources of top-down modulation.

Not all false memories are created equal: The neural basis of false recognition

Rachel J. Garoff-Eaton , Scott D. Slotnick and Daniel L. Schacter

Cerebral Cortex 16:1645-1652 (2006)

False recognition, a type of memory distortion where one claims to remember something that never happened, can occur in response to items that are similar but not identical to previous seen items (i.e., related false recognition) or in response to novel items (i.e., unrelated false recognition). It is unknown whether these 2 types of memory errors arise from the same or distinct neural substrates. Using functional magnetic resonance, we compared the neural activity associated with true recognition, related false recognition, and unrelated false recognition for abstract shapes. True recognition and related false recognition were associated with similar patterns of neural activity, including activity in the prefrontal cortex, the parietal cortex, and the medial temporal lobe. By contrast, unrelated false recognition was associated with activity in language-processing regions. These results indicate that false recognition is not a unitary phenomenon, but rather can reflect the operation of 2 distinct cognitive and neural processes.

Stimulus context modulates competition in human extrastriate cortex

Diane M Beck and Sabine Kastner

Nature Neuroscience 8:1110-1116 (2005)

When multiple stimuli appear simultaneously in the visual field, they are not processed independently, but rather interact in a mutually suppressive way, suggesting that they compete for neural representation in visual cortex. The biased competition model of selective attention predicts that the competition can be influenced by both top-down and bottom-up mechanisms. Directed attention has been shown to bias competition in favor of the attended stimulus in extrastriate cortex. Here, we show that suppressive interactions among multiple stimuli are eliminated in extrastriate cortex when they are presented in the context of pop-out displays, in which a single item differs from the others, but not in heterogeneous displays, in which all items differ from each other. The pop-out effects seemed to originate in early visual cortex and were independent of attention top-down control, suggesting that stimulus context may provide a powerful influence on neural competition in human visual cortex.

Content-specificity of the neural correlates of recollection

C. Chad Woodruff, Jeffrey D. Johnson, Melina R. Uncapher, Michael D. Rugg

Neuropsychologia 43:1022–1032 (2005)

It is widely assumed that episodic retrieval (recollection) involves reinstatement of cortical activity engaged during the processing of an episode when it was initially experienced. It follows from this assumption that the cortical correlates of recollection should differ with the content of what is recollected, and that retrieval of different content should be associated with activity in functionally distinct cortical regions. The present experiment investigated these predictions. Subjects (N=17) studied a mixed list of words and pictures and were then presented with a test list comprised of words only. Test items were studied words, the names of studied pictures, and unstudied (new) words. Functional magnetic resonance images were acquired while the subjects made Remember/Know/New judgments to these words. Independent of study material, studied items endorsed as Remembered elicited greater activity than correctly classified unstudied items in several regions, including left frontal, left lateral parietal, and posterior cingulated cortex. In addition, Remembered items elicited greater activity in the right hippocampus and parahippocampal gyrus than items accorded Know judgments, replicating previous findings. Analysis of content-specific effects demonstrated a regional double-dissociation within left fusiform cortex; recollected words elicited greater activity than recollected pictures in lateral fusiform, whereas the reverse effect was evident in an anterior fusiform region. The lateral and anterior fusiform areas correspond closely to areas held to be functional specialized for the processing of visual words and pictures, respectively. Thus, the current findings support the cortical reinstatement hypothesis of episodic retrieval.

Recollection and the reinstatement of encoding-related cortical activity

Jeffrey D. Johnson and Michael D. Rugg

Cerebral Cortex 17:2507-2515 (2007)

The neural correlates of episodic memory retrieval (“recollection”) differ according to the type of information contained in the recollected episode. Such content-specific recollection effects have been hypothesized to reflect the reinstatement of processes or representations active during encoding. Using event-related functional magnetic resonance imaging, we evaluated this hypothesis by directly contrasting the neural activity elicited during the encoding and subsequent recollection of words studied with one of the 2 encoding tasks. Study words appearing on pictures of scenes required imaging the word’s referent at any location within the scene, whereas words appearing on a blank background required generating a sentence that incorporated the word. On a later memory test, the neural correlates of recollection were operationalized by contrasting the activity elicited during “remember” versus “know” responses. Recollected words from the “scene” task elicited activity in regions of left occipital cortex and anterior fusiform gyrus that overlapped regions where encoding-related activity was greater for the scene than sentence task. Conversely, activity elicited by words recollected from the “sentence” task overlapped with a region of ventromedial frontal cortex where encoding-related activity was greater for the sentence task. These content-specific associations between encoding- and recollection- related neural activity strongly support the reinstatement hypothesis of episodic retrieval.

A voice region in the monkey brain

Christopher I Petkov, Christoph Kayser, Thomas Steudel, Kevin Whittingstall, Mark Augath and Nikos K Logothetis

Nature Neuroscience 11:367-374

For vocal animals, recognizing species-specific vocalization is important for survival and social interactions. In human, a voice region has been identified that is sensitive to human voices and vocalizations. As this region also strongly responds to speech, it is unclear whether it is tightly associated with linguistic processing and is thus unique to humans. Using functional magnetic resonance imaging of macaque monkeys (Old World primates, Macaca mulatta) we discovered a high-level auditory region that prefers species-specific vocalizations over other vocalization and sounds. This region not only showed sensitivity to the “voice” of the species, but also to the vocal identity of conspecific individuals. The monkey voice region is located on the superior-temporal plane and belongs to an anterior auditory “what” pathway. These results establish functional relationships with the human voice region and support the notion that, for different primate species, the anterior temporal regions of the brain are adapted for recognizing communication signals from conspecifics.

Neural correlates of conceptual implicit memory and their contamination of putative neural correlates of explicit memory

Joel L. Voss and Ken A. Paller

Learning and Memory 14: 259-267 (2007)

During episodic recognition tests, meaningful stimuli such as words can engender both conscious retrieval (explicit memory) and facilitated access to meaning that is distinct from the awareness of remembering (conceptual implicit memory). Neuroimaging investigations of one type of memory are frequently subject to the confounding influence of the other type of memory, thus posing a serious impediment to theoretical advances in this area. We used minimalist visual shapes (squiggles) to attempt to overcome this problem. Subjective rating of squiggle meaningfulness varied idiosyncratically, and behavioral indications of conceptual implicit memory were evident only for stimuli given higher ratings. These effects did not result from perceptual-based fluency or from explicit remembering. Distinct event-related brain potentials were associated with conceptual implicit memory and with explicit memory by virtue of contrast based on meaningfulness ratings and memory judgments, respectively. Frontal potentials from 300 to 500 msec after the onset of repeated squiggles varied systematically with perceived meaningfulness. Explicit memory was held constant in this contrast, so these potentials were taken as neural correlates of conceptual implicit memory. Such potentials can contaminate putative neural correlates of explicit memory, in that they are frequently attributed to the expression of explicit memory known as familiarity. These findings provide the first neural dissociation of these two memory phenomena during recognition testing and underscore the necessity of taking both types of memory into account in order to obtain valid neural correlates of specific memory functions.

Validation neural correlates of familiarity

Ken A. Paller, Joel L. Voss and Stephan G. Boehm

TRENDS in Cognitive Sciences 11:243-250 (2007)

Familiarity is a pervasive memory phenomenon that occurs in its most basic form when someone recognizes a repeated stimulus without recollecting other aspects of the requisite prior learning episode. Theoretical controversy currently abounds with respect to both the cognitive and neural characteristics of familiarity. Here, we show that the extant data, particular brain-potential data, are insufficient for validating putative neural correlates of familiarity, and we outline strategies for making progress for this problem. Conceptual priming is an implicit-memory phenomenon that often occurs together with familiarity; experiments that conflate the two phenomena can be misleading. Avoiding this conflation is required to understand familiarity and to determine the extent to which the neurocognitive processes that support priming also drive familiarity..

Action-blindsight in healthy subjects after transcranial magnetic stimulation

Mark Schram Christensen, Lasse Kristiansen, James B. Rowe and Jens Bo Nielsen

PNAS 105:1353-1357 (2008)

Clinical cases of blindsight have shown that visually guided movements can be accomplished without conscious visual perception. Here, we show that blindsight can be induced in healthy subjects by using transcranial magnetic stimulation over the visual cortex. Transcranial magnetic stimulation blocked the conscious perception of a visual stimulus, but subjects still corrected an ongoing reaching movement in response to the stimulus. The data show that correction of reaching movements does not require conscious perception of a visual target stimulus, even in healthy people. Our results support previous results suggesting that an efference copy involved in movement correction, and this mechanism seems to be consistent even for movement correction without perception.