Information Conveyed by Onset Transients in Responses of Striate Cortical Neurons

Abstract

Normal eye movements ensure that the visual world is seen episodically, as a series of often stationary images. In this paper we characterize the responses of neurons in striate cortex to stationary grating patterns presented with abrupt onset. These responses are distinctive. In most neurons the onset of a grating gives rise to a transient discharge that decays with a time constant of 100 msec or less. The early stages of response have higher contrast gain and higher response gain than later stages. Moreover, the variability of discharge during the onset transient is disproportionately low. These factors together make the onset transient an information-rich component of response, such that the detectability and discriminability of stationary gratings grows rapidly to an early peak, within 150 msec of the onset of the response in most neurons. The orientation selectivity of neurons estimated from the first 150 msec of discharge to a stationary grating is indistinguishable from the orientation selectivity estimated from longer segments of discharge to moving gratings. Moving gratings are ultimately more detectable than stationary ones, because responses to the former are continuously renewed. The principal characteristics of the response of a neuron to a stationary grating-the initial high discharge rate, which decays rapidly, and the change of contrast gain with time-are well captured by a model in which each excitatory synaptic event leads to an immediate reduction in synaptic gain, from which recovery is slow.

Modulation of Transient and Sustained Response Components of V4 Neurons by Temporal Crowding in Flashed Stimulus Sequences

“…These severe truncations in the response of neurons are alleviated at ISIs (217 and 327 ms) that mimic a short fixation with no stimulus in the receptive field. Certainly, the low variability of discharge and higher gain relationships associated with the transient components observed under some conditions (Muller et al, 2001) become quite irregular under sequenced flash and presumably saccade conditions. Saccade paradigms confirm that the short ISIs of flashed stimuli mimic aspects of sequences of stimuli appearing in the receptive field as a result of a saccade (Gawne and Martin, 2002).…”

“…Both transient and sustained aspects of neural coding as well as the tuning properties of neurons play important roles in this transformation. The specific loss of the information-rich transient components (Gershon et al, 1998;Mechler et al, 1998;Muller et al, 2001) might underlie some of the decreased ability to identify particular stimuli or stimulus pairs in RSVP paradigms. In addition, the wide variations in response onset latencies caused by the partial or complete loss of the transient component of V4 responses might underlie some identification loss or confusion, particularly if temporal synchronization across different hierarchical areas plays a significant role in stimulus identification (Thorpe et al, 2001).…”

Variability and Correlations in Primary Visual Cortical Neurons Driven by Fixational Eye Movements

“…We also note that the FEMcorrected FF estimates reported by Snodderly and colleagues (ϳ0.3) were substantially smaller than those reported here (ϳ0.85). This difference is likely due to their use of a transient, "optimally tuned" stimulus given that the "onset transients" of visual cortical neurons have been shown to exhibit lower amounts of response variability (Müller et al, 2001;Churchland et al, 2010).…”

Macaque Middle Temporal Neurons Signal Depth in the Absence of Motion

“…Thus, although this issue deserves additional study, we think that our results have considerable bearing on the role of MT in natural three-dimensional (3D) vision. Muller et al (2001) have recently compared the responses of V1 neurons to moving and stationary grating stimuli. Many of our analyses are similar to theirs, and the results from V1 and MT are quite comparable.…”