A neural correlate of visual discomfort from flicker.

The theory of "visual stress" holds that visual discomfort results from overactivation of the visual cortex. Despite general acceptance, there is a paucity of empirical data that confirm this relationship, particularly for discomfort from visual flicker. We examined the association between neural response and visual discomfort using flickering light of different temporal frequencies that separately targeted the LMS, L-M, and S postreceptoral channels.

Confounding of norm-based and adaptation effects in brain responses.

Separate neuroscience experiments have examined two properties of neural coding for perceptual stimuli. Adaptation studies seek a graded recovery from neural adaptation with ever greater dissimilarity between pairs of stimuli. Studies of prototype effects test for a larger absolute response to a stimulus which is distant from the center of a stimulus space.

de Bruijn cycles for neural decoding.

Stimulus counterbalance is critical for studies of neural habituation, bias, anticipation, and (more generally) the effect of stimulus history and context. We introduce de Bruijn cycles, a class of combinatorial objects, as the ideal source of pseudo-random stimulus sequences with arbitrary levels of counterbalance. Neuro-vascular imaging studies (such as BOLD fMRI) have an additional requirement imposed by the filtering and noise properties of the method: only some temporal frequencies of neural modulation are detectable.

Selected contributions to neurology by Philadelphia neurologists since 1980.

On the occasion of the 125th anniversary of the Philadelphia Neurologic Society, 3 short talks were given that highlighted accomplishments by Philadelphia's neurologists over the past 30 years. The theme for the celebration was "Contributions to Neurology by Philadelphia Neurologists, 1980-2008." Each of the 3 speakers was chosen because of his contributions and the sequential time frames in which they occurred.

Temporally distinct neural coding of perceptual similarity and prototype bias.

Psychological models suggest that perceptual similarity can be divided into geometric effects, such as metric distance in stimulus space, and non-geometric effects, such as stimulus-specific biases. We investigated the neural and temporal separability of these effects in a carry-over, event-related potential (ERP) study of facial similarity. By testing this dual effects model against a temporal framework of visual evoked components, we demonstrate that the behavioral distinction between geometric and non-geometric similarity effects is consistent with dissociable neural responses across the time course of face perception.

Neural tuning for face wholes and parts in human fusiform gyrus revealed by FMRI adaptation.

Although the right fusiform face area (FFA) is often linked to holistic processing, new data suggest this region also encodes part-based face representations. We examined this question by assessing the metric of neural similarity for faces using a continuous carryover functional MRI (fMRI) design. Using faces varying along dimensions of eye and mouth identity, we tested whether these axes are coded independently by separate part-tuned neural populations or conjointly by a single population of holistically tuned neurons.

Distinguishing conjoint and independent neural tuning for stimulus features with fMRI adaptation.

A central focus of cognitive neuroscience is identification of the neural codes that represent stimulus dimensions. One common theme is the study of whether dimensions, such as color and shape, are encoded independently by separate pools of neurons or are represented by neurons conjointly tuned for both properties. We describe an application of functional magnetic resonance imaging (fMRI) adaptation to distinguish between independent and conjoint neural representations of dimensions by examining the neural signal evoked by changes in one versus two stimulus dimensions and considering the metric of two-dimension additivity.

The representation of parts and wholes in face-selective cortex.

Although face perception is often characterized as depending on holistic, rather than part-based, processing, there is behavioral evidence for independent representations of face parts. Recent work has linked "face-selective" regions defined with functional magnetic resonance imaging (fMRI) to holistic processing, but the response of these areas to face parts remains unclear. Here we examine part-based versus holistic processing in "face-selective" visual areas using face stimuli manipulated in binocular disparity to appear either behind or in front of a set of stripes [Nakayama, K.

Continuous carry-over designs for fMRI.

This paper describes continuous carry-over fMRI experiments. In these studies, stimuli are presented in an unbroken, sequential manner, and can be used to estimate simultaneously the mean difference in neural activity between stimuli as well as the effect of one stimulus upon another (carry-over effects). Neural adaptation, which has been the basis of many recent fMRI studies, is shown to be a specific form of carry-over effect.