Biomedical subjects

Scott D Slotnick

Publications and source records attributed to Scott D Slotnick.

At least 19 recordsLinked to original sources

PubMed2007

Aging, source memory, and misrecollections.

The authors propose an illusory recollection account of why cognitive aging is associated with episodic memory deficits. After listening to statements presented by either a female or a male speaker, older adults were prone to misrecollecting past events. The authors' illusory recollection account is instantiated in a new illusory recollection signal detection model that provides a better fit of older adults' data than does the standard signal detection model. They observed that age-related differences in source memory (as measured by source d' scores) virtually disappear after accounting for the occurrence of illusory recollections. These data suggest that age-related source memory impairments are not due to older adults' remembering less diagnostic source information and having to guess more. Instead, older adults appear to misremember past events more often than younger adults.

Adolescent↗

PubMed2006

The nature of memory related activity in early visual areas.

Memory for visual items can evoke activity in visual processing regions, which is typically assumed to reflect conscious remembering. However, based on previous findings, we hypothesized that such activity in early visual areas (BA17, BA18) may reflect priming, a form of nonconscious memory. We tested this hypothesis in two fMRI experiments with similar stimulus protocols, but explicit or implicit task instructions. During initial runs, abstract shapes were presented to either side of fixation, filled with parallel lines of random orientation and color. In subsequent runs, old and new shapes (plus related shapes in Experiment 2) were presented at fixation. In Experiment 1, participants were instructed to remember each shape and its spatial location during initial runs; during subsequent runs they classified each shape as old and on the "left", old and on the "right", or "new". A right fusiform gyrus region (BA18) and a left lingual gyrus region (BA18) were preferentially associated with shapes previously presented on the left and right, respectively. In support of our hypothesis, this early visual area activity was independent of response accuracy for spatial location. In Experiment 2, for each shape, participants identified parallel line orientation relative to horizontal. Consistent with our hypothesis, specific neural activity was observed in early visual regions (BA17, BA18, extending into BA19), with old activity greater than related and new activity (likely reflecting priming). The results of these experiments provide convergent evidence that memory related early visual area activity (BA17, BA18) can reflect nonconscious processing.

Adult↗

PubMed2006

Prefrontal cortex hemispheric specialization for categorical and coordinate visual spatial memory.

During visual spatial perception of multiple items, the left hemisphere has been shown to preferentially process categorical spatial relationships while the right hemisphere has been shown to preferentially process coordinate spatial relationships. We hypothesized that this hemispheric processing distinction would be reflected in the prefrontal cortex during categorical and coordinate visual spatial memory, and tested this hypothesis using functional magnetic resonance imaging (fMRI). During encoding, abstract shapes were presented in the left or right hemifield in addition to a dot at a variable distance from the shape (with some dots on the shape); participants were instructed to remember the position of each dot relative to the shape. During categorical memory retrieval, each shape was presented centrally and participants responded whether the previously corresponding dot was 'on' or 'off' of the shape. During coordinate memory retrieval, each shape was presented centrally and participants responded whether the previously corresponding dot was 'near' or 'far' from the shape (relative to a reference distance). Consistent with our hypothesis, a region in the left prefrontal cortex (BA10) was preferentially associated with categorical visual spatial memory and a region in the right prefrontal cortex (BA9/10) was preferentially associated with coordinate visual spatial memory. These results have direct implications for interpreting previous findings that the left prefrontal cortex is associated with source memory, as this cognitive process is categorical in nature, and the right prefrontal cortex is associated with item memory, as this process depends on the precise spatial relations among item features or components.

Adult↗

PubMed2006

Temporally unfolding neural representation of pictorial occlusion.

The human visual system possesses a remarkable ability to reconstruct the shape of an object that is partly occluded by an interposed surface. Behavioral results suggest that, under some circumstances, this perceptual process (termed amodal completion) progresses from an initial representation of local image features to a completed representation of a shape that may include features that are not explicitly present in the retinal image. Recent functional magnetic resonance imaging (fMRI) studies have shown that the completed surface is represented in early visual cortical areas. We used fMRI adaptation, combined with brief, masked exposures, to track the amodal completion process as it unfolds in early visual cortical regions. We report evidence for an evolution of the neural representation from the image-based feature representation to the completed representation. Our method offers the possibility of measuring changes in cortical activity using fMRI over a time scale of a few hundred milliseconds.

Brain↗

PubMed2005

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

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 previously 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 imaging, 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.

Adolescent↗

PubMed2005

Visual mental imagery induces retinotopically organized activation of early visual areas.

There is a long-standing debate as to whether visual mental imagery relies entirely on symbolic (language-like) representations or also relies on depictive (picture-like) representations. We sought to discover whether visual mental imagery could evoke cortical activity with precise visual field topography (retinotopy). Participants received three conditions: the perception condition consisted of a standard retinotopic mapping procedure, where two flickering checkerboard wedges rotated around a central fixation point. The imagery and attention conditions consisted of the same stimulus, but only the outer arcs of the wedges were visible. During imagery, participants mentally reproduced the stimulus wedges, using the stimulus arcs as a guide. The attention condition required either distributed attention or focused attention to where the stimulus wedges would have been. Event-related analysis revealed that the imagery (greater than either form of attention) retinotopic maps were similar to the perception maps. Moreover, blocked analysis revealed similar perception and imagery effects in human motion processing region MT+. These results support the depictive view of visual mental imagery.

Adult↗

PubMed2005

Common neural substrates for the control and effects of visual attention and perceptual bistability.

Behavioral studies have suggested that bistable figure perception is mediated by spatial attention. We tested this hypothesis using event-related functional MRI. During central fixation, two tilted squares containing coherently moving dots were presented in the left and right hemifields. In the attention condition, participants were occasionally cued to shift attention between the squares. In the perception condition, corresponding corners of the squares were connected by horizontal lines producing a perceptually bistable Necker cube figure. Observers reported which of the two faces appeared 'forward' in depth; cues elicited voluntary perceptual reversals. Attending to either square during the attention condition or perceiving either square as forward during the perception condition yielded increased activity in contralateral visual areas. Furthermore, voluntary shifts of attention and voluntary shifts in perceptual configuration were associated with common activity in the posterior parietal cortex, part of the frontoparietal attentional control network. These results support the hypothesis that voluntary shifts in perceptual bistability are mediated by spatial attention.

Acoustic Stimulation↗

PubMed2005

Support for a continuous (single-process) model of recognition memory and source memory.

Does memory retrieval occur in a continuous or an all-or-none manner? The shape of the receiver operating characteristic (ROC) has been used to answer this question, with curvilinear and linear memory ROCs indicating continuous and all-or-none retrieval processes, respectively. Signal detection models (e.g., the unequal variance model) correspond to a continuous retrieval process, whereas threshold models (including the multinomial model and the recollection component of the dual-process model) correspond to an all-or-none process. In studies of source memory, Slotnick et al. (2000) and others have observed curvilinear ROCs (supporting the unequal variance model), whereas Yonelinas (1999) observed linear ROCs (supporting the dual-process model). We resolve these seemingly inconsistent results, showing that source memory ROCs are naturally curvilinear but can appear linear when nondiagnostic source information is included in the analysis. Furthermore, the unequal variance model accounted for both recognition memory and source memory ROCs, supporting a continuous process of memory retrieval.

Humans↗

PubMed2004

The neural origins of specific and general memory: the role of the fusiform cortex.

Recognition of an object can be based on memory for specific details of a prior encounter with the object, or on a more general memory for the type of object previously encountered. Responding on the basis of general information alone can sometimes produce memory errors involving both distortion and forgetting, but little is known about the neural origins of general versus specific recognition. We extended the standard subsequent memory paradigm to examine whether neural activity at encoding predicts whether an object will subsequently elicit specific as compared to general memory. During event-related functional magnetic resonance imaging (fMRI), participants viewed objects and made size judgments about them. Later, they viewed same, similar, and new objects, labeling each as "same," "similar," or "new." Specific recognition was indicated by a "same" response to a same object. By contrast, general, non-specific recognition was indicated by either a "same" response to a similar object (false memory) or a "similar" response to a same object (partial memory). As predicted, specific recognition, as compared to non-specific recognition, was associated with encoding-related activity in the right fusiform cortex, while non-specific recognition, as compared to forgetting, was associated with encoding-related activity in the left fusiform cortex. Furthermore, all successful recognition (specific and general), as compared to forgetting, was associated with encoding-related activity in bilateral fusiform cortex. These results suggest that the right fusiform cortex is associated with specific feature encoding, while the left fusiform cortex is involved in more general object encoding.

Adult↗

PubMed2004

The cognitive neuroscience of memory distortion.

Memory distortion occurs in the laboratory and in everyday life. This article focuses on false recognition, a common type of memory distortion in which individuals incorrectly claim to have encountered a novel object or event. By considering evidence from neuropsychology, neuroimaging, and electrophysiology, we address three questions. (1) Are there patterns of neural activity that can distinguish between true and false recognition? (2) Which brain regions contribute to false recognition? (3) Which brain regions play a role in monitoring or reducing false recognition? Neuroimaging and electrophysiological studies suggest that sensory activity is greater for true recognition compared to false recognition. Neuropsychological and neuroimaging results indicate that the hippocampus and several cortical regions contribute to false recognition. Evidence from neuropsychology, neuroimaging, and electrophysiology implicates the prefrontal cortex in retrieval monitoring that can limit the rate of false recognition.

Animals↗

PubMed2004

A sensory signature that distinguishes true from false memories.

Human behavioral studies show that there is greater sensory/perceptual detail associated with true memories than false memories. We therefore hypothesized that true recognition of abstract shapes would elicit greater visual cortical activation than would false recognition. During functional magnetic resonance imaging (fMRI), participants studied exemplar shapes and later made recognition memory decisions ("old" or "new") concerning studied exemplars (old shapes), nonstudied lures (related shapes) and new shapes. Within visual processing regions, direct contrasts between true recognition ("old" response to an old shape; old-hit) and false recognition ("old" response to a related shape; related-false alarm) revealed preferential true recognition-related activity in early visual processing regions (Brodmann area (BA)17, BA18). By comparison, both true and false recognition were associated with activity in early and late (BA19, BA37) visual processing regions, the late regions potentially supporting "old" responses, independent of accuracy. Further analyses suggested that the differential early visual processing activity reflected repetition priming, a type of implicit memory. Thus, the sensory signature that distinguishes true from false recognition may not be accessible to conscious awareness.

Adult↗

PubMed2004

Human MT+ mediates perceptual filling-in during apparent motion.

During apparent motion, spatially distinct items presented in alternation cause the perception of a visual stimulus smoothly traversing the intervening space where no physical stimulus exists. We used fMRI to determine whether the perceptual 'filling-in' that underlies this phenomenon has an early or late cortical locus. Subjects viewed a display comprised of concentric rings that elicited apparent motion (two concentric rings presented in alternation), flicker (the same rings presented simultaneously), or real motion. We independently localized the cortical regions corresponding to the path of apparent motion in early visual areas (V1, V2, VP, V3, V4v, V3A), as well as the human motion processing complex (MT+). Cortical activity in the path of apparent motion in early visual areas was similar in amplitude during both apparent motion and flicker. In contrast, cortical activity in MT+ was higher in amplitude during apparent motion than during flicker, but was lower in amplitude than during real motion. In addition, we observed overlap in the cortical loci of MT+ and the lateral occipital complex (LOC), a region involved in shape and object processing. This overlap suggests that these regions could directly interact and thereby support perceived object continuity during apparent motion.

Adult↗

PubMed2004

Visual memory and visual perception recruit common neural substrates.

This human neuroimaging review aims to determine the degree to which visual memory evokes activity in neural regions that have been associated with visual perception. A visual perception framework is proposed to identify cortical regions associated with modality-specific processing (i.e., visual, auditory, motor, or olfactory), visual domain-specific processing (i.e., "what" versus "where," or face versus visual context), and visual feature-specific processing (i.e., color, motion, or spatial location). Independent assessments of visual item memory studies and visual working memory studies revealed activity in the appropriate cortical regions associated with each of the three levels of visual perception processing. These results provide compelling evidence that visual memory and visual perception are associated with common neural substrates. Furthermore, as with visual perception, they support the view that visual memory is a constructive process, in which features or components from disparate cortical regions bind together to form a coherent whole.

Cerebral Cortex↗

PubMed2003

Retinotopic mapping reveals extrastriate cortical basis of homonymous quadrantanopia.

It has been conventionally assumed that cortically based quadrantic visual field deficits (homonymous quadrantanopias) are caused by lesions in striate cortex (V1), extending precisely to the horizontal meridian representation. A more recent model, supported by anatomic MRI evidence, consists of an exclusively extrastriate cortical basis (e.g. V2, V3, VP, V4v). Employing fMRI, we sought to distinguish between these models through retinotopic mapping of a patient with an upper right homonymous quadrantanopia. As expected, maps of the lower right quadrant and left hemifield were normal. The map corresponding to the impaired upper right quadrant was normal in V1 and V2, with little or no activity in VP and V4v. These results provide functional evidence that extrastriate cortical lesions can elicit homonymous quadrantanopias.

Brain Mapping↗

PubMed2003

Efficient acquisition of human retinotopic maps.

A bifield stimulation method for rapidly obtaining retinotopic maps in human occipital cortex using functional MRI was compared to conventional unifield stimulation. While maintaining central fixation, each participant viewed the conventional display, consisting of a single rotating checkerboard wedge and, in a separate run, the bifield display, consisting of two symmetrically placed rotating checkerboard wedges (a "propeller" configuration). Both stimulus configurations used wedges with 30 degree polar angle width, 6.8 degrees visual angle extension from fixation, and 8.3 Hz contrast polarity reversal rate. Retinotopic maps in each condition were projected onto a distortion corrected computationally flattened cortical surface representation obtained from a high-resolution structural MRI. An automated procedure to localize borders between early visual areas revealed, as expected, that map precision increased with duration of data acquisition for both conditions. Bifield stimulation required 40% less time to yield maps with similar precision to those obtained using conventional unifield stimulation.

Brain Mapping↗

PubMed2003

Distinct prefrontal cortex activity associated with item memory and source memory for visual shapes.

In contrast to item memory, which refers to recognition or recall of previously presented information, source memory refers to memory for the context of previously presented information. The relatively few functional MRI (fMRI) source memory studies conducted to date have provided evidence that item memory and source memory are associated with differential activity in right and left prefrontal cortex, respectively. To both confirm this distinction in prefrontal cortex and to determine whether other differences in the neural substrates associated with these cognitive functions exist, an event-related fMRI study was conducted. In this study, item memory and source memory encoding phases were identical; participants viewed a series of abstract visual shapes presented on the left or right side of the screen and were instructed to remember each shape and its spatial location. During the item memory retrieval phase, shapes from the encoding phase were intermixed with new shapes and participants made an old-new judgment. During the source memory retrieval phase, all shapes were from the encoding phase and participants made a left-right judgment. An event-related analysis of item memory and source memory revealed a right and left prefrontal cortex distinction. Moreover, only item memory was associated with activity in the medial temporal lobes. These results confirm and extend previous findings that item memory and source memory are associated with distinct neural substrates.

Adult↗

PubMed2003

Attentional inhibition of visual processing in human striate and extrastriate cortex.

Allocating attention to a spatial location in the visual field is associated with an increase in the cortical response evoked by a stimulus at that location, compared to when the same stimulus is unattended. We used event-related functional magnetic resonance imaging to investigate attentional modulation of the cortical response to a stimulus probe at an attended location and to multiple probes at unattended locations. A localizer task and retinotopic mapping were used to precisely identify the cortical representations of each probe within striate (V1) and extrastriate cortex (V2, VP, V3, V4v, and V3A). The magnitude and polarity of attentional modulation were assessed through analysis of event-related activity time-locked to shifts in spatial attention. Attentional facilitation at the attended location was observed in striate and extrastriate cortex, corroborating earlier findings. Attentional inhibition of visual stimuli near the attended location was observed in striate cortex, and attentional inhibition of more distant stimuli occurred in both striate and extrastriate cortex. These findings indicate that visual attention operates both through facilitation of visual processing at the attended location and through inhibition of unattended stimulus representations in striate and extrastriate cortex.

Adult↗

PubMed2003

Cortical mechanisms of feature-based attentional control.

A network of fronto-parietal cortical areas is known to be involved in the control of visual attention, but the representational scope and specific function of these areas remains unclear. Recent neuroimaging evidence has revealed the existence of both transient (attention-shift) and sustained (attention-maintenance) mechanisms of space-based and object-based attentional control. Here we investigate the neural mechanisms of feature-based attentional control in human cortex using rapid event-related functional magnetic resonance imaging (fMRI). Subjects viewed an aperture containing moving dots in which dot color and direction of motion changed once per second. At any given moment, observers attended to either motion or color. Two of six motion directions and two of six colors embedded in the stimulus stream cued subjects either to shift attention from the currently attended to the unattended feature or to maintain attention on the currently attended feature. Attentional modulation of the blood oxygenation level dependent (BOLD) fMRI signal was observed in early visual areas that are selective for motion and color. More importantly, both transient and sustained BOLD activity patterns were observed in different fronto-parietal cortical areas during shifts of attention. We suggest these differing temporal profiles reflect complementary roles in the control of attention to perceptual features.

Action Potentials↗