Biomedical subjects

S Friedman-Hill

Publications and source records attributed to S Friedman-Hill.

3 recordsLinked to original sources

PubMed2000

Dynamics of striate cortical activity in the alert macaque: I. Incidence and stimulus-dependence of gamma-band neuronal oscillations.

Using single and multiunit recordings in the striate cortex of alert macaque monkeys, we find that gamma-band (20-70 Hz) oscillations in neuronal firing are a prominent feature of V1 neuronal activity. The properties of this rhythmic activity are very similar to those previously observed in the cat. Gamma-band activity is strongly dependent on visual stimulation, largely absent during spontaneous activity and, under the conditions of our experiment, not time-locked to the vertical refresh of the computer monitor (80 Hz) used to present the stimuli. In our sample, 61% of multiunit activity (MUA) and 46% of single-unit activity (SUA) was significantly oscillatory, with mean frequencies of 48+/-9 and 42+/-13 Hz, respectively. Gamma-band activity was most likely to occur when cells were activated by their optimal stimuli, but still occurred, although less often and with lower amplitude, in response to nonoptimal stimuli. The frequency of gamma-band activity also reflected stimulus properties, with drifting gratings evoking higher-frequency oscillations than stationary gratings. As in the cat, the spike trains of single cells showing gamma-band oscillations often displayed a pattern of repetitive burst firing, with intraburst firing rates of 300-800 Hz. The overall similarity of rhythmic neuronal activity in the primary visual cortex of cats and monkeys suggests that the phenomenon is not species-specific. The stimulus-dependence of the rhythmic activity is consistent with a functional role in visual perception.

Action Potentials↗

PubMed2000

Dynamics of striate cortical activity in the alert macaque: II. Fast time scale synchronization.

Synchronous neuronal activity with millisecond precision has been postulated to contribute to the process of visual perceptual grouping. We have performed multineuron recordings in striate cortex of two alert macaque monkeys to determine if the occurrence and properties of this form of activity are consistent with the minimal requirements of this theory. We find that neuronal synchronization with millisecond precision is a prevalent and robust feature of stimulus-evoked activity in striate cortex. It occurs among adjacent cells recorded by the same electrode (<120 microm), among cells recorded at separate but nearby sites (300-400 microm) and between cells recorded at locations separated by 3-4 mm. The magnitude and probability of synchronous firing is inversely related to the spatial separation between the cells and it occurs within and between groups of cells that are both tuned and untuned for stimulus orientation and direction. Among those tuned for orientation, cell pairs separated by <400 microm showed no clear dependence of correlated firing on orientation preference. The occurrence of gamma-band (20-70 Hz) oscillations in the cellular firing patterns was a strong predictor of synchronous firing at each of the spatial scales. Nearly 90% of the cell pairs showing significant correlation also showed oscillatory firing in one or both cells of the pair. These results are consistent with some, but not all, of the previous reports of synchronous activity in striate cortex of both cat and primates. The similarities in the properties of synchronous oscillations in the monkey and cat suggest that this form of neuronal activity is a general property of mammalian striate cortex. The relation between correlation and oscillation suggests that neuronal rhythmicity is an important mechanism contributing to synchronization.

Action Potentials↗

PubMed1995

Second-order parallel processing: visual search for the odd item in a subset.

Visual search tasks in which participants searched for an odd element in a subset of items were investigated. Participants searched for an item of odd orientation in the red subset. The target was a red line of X degree, distractors were green lines of X degree and red lines of Y degree. The orientations, X and Y, changed on every trial. In this task, orientation information was useful only after color had been used to select the relevant subset. Results show that response time (RT) and error data were different from standard color X orientation conjunction searches (Experiment 1). RT x Set Size functions had slopes near 0 ms per item (Experiment 2). The selection of the subset appeared to take 200-300 ms (Experiments 2 and 3). Subset selection was based on properties of the relevant subset, not the irrelevant subset (Experiment 4). It was more difficult (perhaps impossible) to select a subset defined by 2 colors (Experiment 5). Random variation in an irrelevant dimension did not disrupt subset search (Experiment 6).

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