Biomedical subjects

Vincent A Billock

Publications and source records attributed to Vincent A Billock.

3 recordsLinked to original sources

PubMed2004

What do catastrophic visual binding failures look like?

Ordinary vision is considered a binding success: all the pieces and aspects of an image are bound together, despite being processed by many different neurons in several different cortical areas. How this is accomplished is a key problem in visual neuroscience. The study of visual binding might be facilitated if we had ways to induce binding failures. A particularly interesting failure would involve a loss of the physical integrity of the image. Here, we identify conditions that induce such perceptual failures (e.g. the melting together of equiluminant colored images and the fragmentation of retinally stabilized images) and we suggest that these should studied using electrophysiological measures of binding.

Animals↗

PubMed2003

Spatiotemporal characteristics of hemodynamic changes in the human lateral prefrontal cortex during working memory tasks.

The prefrontal cortex (PFC) is widely believed to subserve mental manipulation and monitoring processes ascribed to the central executive (CE) of working memory (WM). We attempted to examine and localize the CE by functional imaging of the frontal cortex during tasks designed to require the CE. Using near-infrared spectroscopy, we studied the spatiotemporal dynamics of oxygenated hemoglobin (oxy-Hb), an indicator of changes in regional cerebral blood flow, in both sides of lateral PFC during WM intensive tasks. In most participants, increases in oxy-Hb were localized within one subdivison during performance of the n-back task, whereas oxy-Hb increased more diffusely during the random number generation (RNG) task. Activation of the ventrolateral PFC (VLPFC) was prominent in the n-back task; both sustained and transient dynamics were observed. Transient dynamics means that oxy-Hb first increases but then decreases to less than 50% of the peak value or below the baseline level before the end of the task. For the RNG task sustained activity was also observed in the dorsolateral PFC (DLPFC), especially in the right hemisphere. However, details of patterns of activation varied across participants: subdivisions commonly activated during performance of the two tasks were the bilateral VLPFCs, either side of the VLPFC, and either side of the DLPFC in 4, 2, and 4 of the 12 participants, respectively. The remaining 2 of the 12 participants had no regions commonly activated by these tasks. These results suggest that although the PFC is implicated in the CE, there is no stereotyped anatomical PFC substrate for the CE.

Adult↗

PubMedDate not supplied

A role for cortical crosstalk in the binding problem: stimulus-driven correlations that link color, form, and motion.

The putative independence of cortical mechanisms for color, form, and motion raises the binding problem-how is neural activity coordinated to create unified and correctly segmented percepts? Binding could be guided by stimulus-driven correlations between mechanisms, but the nature of these correlations is largely unexplored and no one has (intentionally) studied effects on binding if this joint information is compromised. Here, we develop a theoretical framework which: (1) describes crosstalk-generated correlations between cortical mechanisms for color, achromatic form, and motion, which arise from retinogeniculate encoding; (2) shows how these correlations can facilitate synchronization, segmentation, and binding; (3) provides a basis for understanding perceptual oddities and binding failures that occur for equiluminant and stabilized images. These ideas can be tested by measuring both perceptual events and neural activity while achromatic border contrast or stabilized image velocity is manipulated.

Animals↗