Biomedical subjects

David Carmel

Publications and source records attributed to David Carmel.

4 recordsLinked to original sources

PubMed2006

Conscious awareness of flicker in humans involves frontal and parietal cortex.

Even when confined to the same spatial location, flickering and steady light evoke very different conscious experiences because of their distinct temporal patterns. The neural basis of such differences in subjective experience remains uncertain . Here, we used functional MRI in humans to examine the neural structures involved in awareness of flicker. Participants viewed a single point source of light that flickered at the critical flicker fusion (CFF) threshold, where the same stimulus is sometimes perceived as flickering and sometimes as steady (fused) . We were thus able to compare brain activity for conscious percepts that differed qualitatively (flickering or fused) but were evoked by identical physical stimuli. Greater brain activation was observed on flicker (versus fused) trials in regions of frontal and parietal cortex previously associated with visual awareness in tasks that did not require detection of temporal patterns . In contrast, greater activation was observed on fused (versus flicker) trials in occipital extrastriate cortex. Our findings indicate that activity of higher-level cortical areas is important for awareness of temporally distinct visual events in the context of a nonspatial task, and they thus suggest that frontal and parietal regions may play a general role in visual awareness.

Adult↗

PubMed2003

Estimating the validity of the guilty knowledge test from simulated experiments: the external validity of mock crime studies.

This experiment was designed to examine the external validity of the standard mock-crime procedure used extensively to evaluate the validity of polygraph tests. The authors manipulated the type of mock-crime procedure (standard vs. a more realistic version) and the time of test (immediate vs. delayed) and examined their effects on the validity of the Guilty Knowledge Test (GKT) and the recall rate of the relevant items. The results indicated that only the type of mock-crime affected the 2 outcome variables. The realistic procedure was associated with a lower recall rate and weaker detection efficiency than the standard procedure. However, these effects were mediated by the type of GKT questions used. Practical implications of these results are discussed.

Adult↗

PubMed2002

Domain specificity versus expertise: factors influencing distinct processing of faces.

To explore face specificity in visual processing, we compared the role of task-associated strategies and expertise on the N170 event-related potential (ERP) component elicited by human faces with the ERPs elicited by cars, birds, items of furniture, and ape faces. In Experiment 1, participants performed a car monitoring task and an animacy decision task. In Experiment 2, participants monitored human faces while faces of apes were the distracters. Faces elicited an equally conspicuous N170, significantly larger than the ERPs elicited by non-face categories regardless of whether they were ignored or had an equal status with other categories (Experiment 1), or were the targets (in Experiment 2). In contrast, the negative component elicited by cars during the same time range was larger if they were targets than if they were not. Furthermore, unlike the posterior-temporal distribution of the N170, the negative component elicited by cars and its modulation by task were more conspicuous at occipital sites. Faces of apes elicited an N170 that was similar in amplitude to that elicited by the human face targets, albeit peaking 10 ms later. As our participants were not ape experts, this pattern indicates that the N170 is face-specific, but not specie-specific, i.e. it is elicited by particular face features regardless of expertise. Overall, these results demonstrate the domain specificity of the visual mechanism implicated in processing faces, a mechanism which is not influenced by either task or expertise. The processing of other objects is probably accomplished by a more general visual processor, which is sensitive to strategic manipulations and attention.

Adult↗

PubMed2002

Accounts for the N170 face-effect: a reply to Rossion, Curran, & Gauthier.

In their commentary, Rossion, Curran, and Gauthier (Rossion, B., Curran, T., Gauthier, I. (2002). A defense of the subordinate-level expertise account for the N170 component. Cognition, 85, 197-202) (RC&G) raise a series of arguments against the domain-specificity account for the N170 face-effect (Carmel, D., & Bentin, S. (2002). Domain specificity versus expertise: factors influencing distinct processing of faces. Cognition, 83, 1-29). This effect consists of a large difference (always significant) observed in the amplitude of a negative component peaking at the lower posterior-temporal sites in response to human faces relative to many other stimulus categories. As an alternative to domain specificity, RC&G advocate a "subordinate-level expertise" account, by which the N170 effect can be obtained for any type of stimulus for the individual identification of which the perceiver is an expert. While considering some of their arguments well taken and interesting, we believe that, overall, RC&G's interpretation of our current data (as well as some of theirs) and of our position ignores several important aspects and, therefore, their critique is not persuasive.

Brain Mapping↗