Solid Phase Synthesis of a Functionalized Bis-Peptide Using …
Published 5/15/2012
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In JoVE (1)
Other Publications (13)
Articles by David Carmel in JoVE
How to Create and Use Binocular Rivalry
1Department of Psychology, New York University, 2Centre for Neural Science, New York University, 3Department of Psychology, Princeton University, 4Neuroscience Institute, Princeton University
Binocular rivalry occurs when the eyes are presented with different images at the same location: one image dominates while the other is suppressed, and dominance alternates periodically. Rivalry is useful for investigating perceptual selection and visual awareness. Here we describe several easy methods for creating and using binocular rivalry stimuli.
Other articles by David Carmel on PubMed
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.
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.
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.
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.
Perceptual Load Modulates Conscious Flicker Perception
Subjective visual experience depends not only on the spatial arrangement of the environment, but also on the temporal pattern of stimulation. For example, flickering and steady light presented in the same location evoke a very different perceptual experience due to their different temporal patterns. Here, we examined whether the availability of processing resources affected the temporal resolution of conscious flicker perception--the ability to distinguish rapid changes in light intensity, detecting visual temporal patterns. Participants detected flicker in a fixated LED that flickered at or around the individually adjusted critical flicker fusion (CFF) threshold while searching for a target letter presented in the periphery either on its own (low perceptual load) or among other letters (high load). Physically identical flickering stimuli were more likely to be perceived as "fused" under high (compared to low) load in the peripheral letter search. Furthermore, psychophysical measures showed a reduction in flicker detection sensitivity under high perceptual load. These results could not be due to criterion or stimulus prioritization differences or to differential likelihood of forgetting the correct response under different load conditions. These findings demonstrate that perceptual load influences conscious perception of temporal patterns.
Perceptual Learning and Dynamic Changes in Primary Visual Cortex
Perceptual learning is the improved performance that follows practice in a perceptual task. In this issue of Neuron, Yotsumoto et al. use fMRI to show that stimuli presented at the location used in training initially evoke greater activation in primary visual cortex than stimuli presented elsewhere, but this difference disappears once learning asymptotes.
Unconscious Orientation Processing Depends on Perceptual Load
The effects of perceptual load on the level of adaptation to task-irrelevant and invisible oriented gratings were examined. Participants performed a task at fixation under conditions of low (detecting color targets) or high (detecting conjunctions of color and shape) perceptual load. Simultaneously, a task-irrelevant-oriented grating was presented monocularly in a more peripheral location but was suppressed from awareness by flashing a dynamic mask stimulus at the same retinal location in the other eye. Orientation-specific adaptation to the invisible irrelevant grating was found at low perceptual load but was eliminated with high perceptual load. These results demonstrate that early unconscious processing of orientation depends on the allocation of limited attentional capacity, and conversely that the allocation of attentional capacity under low (versus high) load is insufficient to bring orientation representations to awareness.
Spatial Attention Can Modulate Unconscious Orientation Processing
It has recently been suggested that visual spatial attention can only affect consciously perceived events. We measured the effects of sustained spatial attention on orientation-selective adaptation to gratings, rendered invisible by prolonged interocular suppression. Spatial attention augmented the orientation-selective adaptation to invisible adaptor orientation. The effect of attention was clearest for test stimuli at peri-threshold, intermediate contrast levels, suggesting that previous negative results were due to assessing orientation discrimination at maximum contrast. On the basis of these findings we propose a constrained hypothesis for the difference between neuronal mechanisms of spatial attention in the presence versus absence of awareness.
Murder, She Wrote: Enhanced Sensitivity to Negative Word Valence
Enhanced sensitivity to information of negative (compared to positive) valence has an adaptive value, for example, by expediting the correct choice of avoidance behavior. However, previous evidence for such enhanced sensitivity has been inconclusive. Here we report a clear advantage for negative over positive words in categorizing them as emotional. In 3 experiments, participants classified briefly presented (33 ms or 22 ms) masked words as emotional or neutral. Categorization accuracy and valence-detection sensitivity were both higher for negative than for positive words. The results were not due to differences between emotion categories in either lexical frequency, extremeness of valence ratings, or arousal. These results conclusively establish enhanced sensitivity for negative over positive words, supporting the hypothesis that negative stimuli enjoy preferential access to perceptual processing.
Right Parietal TMS Shortens Dominance Durations in Binocular Rivalry
Binocular rivalry occurs when dissimilar images are presented to each eye. Rather than a combined picture being perceived, each monocular image competes for perceptual dominance, becoming visible for a few seconds while the other is suppressed. Stable visual input thus leads to alternations in conscious perception, dissociating stimulation from awareness. This makes rivalry particularly useful for elucidating the neural processes underlying consciousness [1]. Retinotopic visual cortex [2] and lateral geniculate nucleus [3] activity are modulated by such alternating perception, implying an early locus for rivaling neural representations. However, higher cortical regions, including right superior parietal cortex, exhibit activity that is time-locked to perceptual transitions [4]. Though this implies the involvement of top-down processes in rivalry, the correlational nature of neuroimaging precludes the attribution of a causal role to such activity, which may instead simply reflect orientating attention to the transition. Here we distinguish these two hypotheses by showing that repetitive transcranial magnetic stimulation (rTMS) over right superior parietal cortex shortened binocular rivalry dominance durations. This suggests that right parietal cortex maintains the current perceptual state during rivalry.
Perceptual Load Alters Visual Excitability
Increasing perceptual load reduces the processing of visual stimuli outside the focus of attention, but the mechanism underlying these effects remains unclear. Here we tested an account attributing the effects of perceptual load to modulations of visual cortex excitability. In contrast to stimulus competition accounts, which propose that load should affect simultaneous, but not sequential, stimulus presentations, the visual excitability account makes the novel prediction that load should affect detection sensitivity for both simultaneous and sequential presentations. Participants fixated a stimulus stream, responding to targets defined by either a color (low load) or color and orientation conjunctions (high load). Additionally, detection sensitivity was measured for a peripheral critical stimulus (CS) presented occasionally. Increasing load at fixation reduced sensitivity to the peripheral CSs; this effect was similar regardless of whether CSs were presented simultaneously with central stimuli or during the (otherwise empty) interval between them. Controls ruled out explanations of the results in terms of strategic task prioritization. These findings support a cortical excitability account for perceptual load, challenging stimulus competition accounts.