Macaque V2 Neurons, But Not V1 Neurons, Show Choice-Related Activity

Abstract

In the macaque extrastriate cortex, robust correlations between perceptual choice and neuronal response have been demonstrated, frequently quantified as choice probabilities (CPs). Such correlations are modest in early visual cortex, suggesting that CPs may depend on the position of a neuron in the hierarchy of visual processing. However, previous studies have not compared neurons with similar precision in equivalent tasks.We investigated the role of cortical hierarchy on CP using a task for which significant CPs have been described previously for middle temporal area (MT). We measured CPs in disparity-selective neurons from both V1 and V2. The stimulus was a dynamic random dot stereogram, presented with a near or a far disparity, masked by varying numbers of binocularly uncorrelated dots. Two macaque monkeys reported whether they perceived a circular patch in front or behind a surrounding annulus in a forced choice task.For V2 (n ϭ 69), CP was on average 0.56, the first demonstration of systematic CPs in a visual area as early as V2. In V1 (n ϭ 74), average CP was at chance level (0.51). The pattern was similar in a subgroup of neurons selected such that the statistical precision in the task was on average identical to that reported for MT (mean CP, 0.51 for V1, n ϭ 33; 0.58 for V2, n ϭ 54). This difference between V1 and V2 could not be explained by eye movements, stimulus size relative to the receptive field, or differences in disparity tuning. Rather, it seems to reflect a functional difference (at least in disparity processing) between striate and extrastriate cortex.

The Functional Link between Area MT Neural Fluctuations and Detection of a Brief Motion Stimulus

“…Although our brief stimulus was designed to minimize non-causal contributions, our DP scores were similar, if not larger, than most reported choice probability scores (Celebrini and Newsome, 1994;Britten et al, 1996;Parker and Newsome, 1998;Dodd et al, 2001;Parker et al, 2002;Williams et al, 2003;Krug, 2004;Krug et al, 2004;Uka and DeAngelis, 2004;Liu and Newsome, 2005;Purushothaman and Bradley, 2005;Nienborg and Cumming, 2006Gu et al, 2008;Law and Gold, 2008;Cohen and Newsome, 2009;Sasaki and Uka, 2009;Price and Born, 2010). The likely reason is that the concentrated burst of firing in response to the motion pulse contained the only available information for successfully performing the task.…”

Psychophysically measured task strategy for disparity discrimination is reflected in V2 neurons

“…This then allowed us to investigate whether this perceptual strategy was reflected in the neuronal response in disparity selective V2 neurons. For this, we reexamined previously reported data 14 .…”

“…The distributions of | symmetry-phase| for near and far-preferring neurons were not significantly different (P = 0.49, Kolmogorov-Smirnov test). We quantified the neuronal thresholds as described previously 5,16 , see 14 . The mean neuronal threshold for the task was slightly lower for the far-preferring neurons (mean threshold 36% ±17%) than the near-preferring neurons (mean 44% ±19%), although this difference was not statistically significant (P = 0.14, t-test).…”

“…Most of the physiological data presented here are further analyses of data for which the recording procedure was fully described in 14 . Briefly, we recorded extracellular activity from disparity selective single-units in V2.…”

Disparity Channels in Early Vision

“…Moreover, several studies indicate that the representation of disparity in V1 cannot account for key aspects of depth perception (Cumming and Parker, 1997Nienborg and Cumming, 2006b). …”