The response of cortical neurons to sensory stimuli is shaped both by past events (adaptation) and the expectation of future events (prediction). Here we employed a visual stimulus paradigm with different levels of predictability to characterise how expectation influences orientation selectivity in the primary visual cortex (V1) of male mice. We recorded neuronal activity using two-photon calcium imaging (GCaMP6f) while animals viewed sequences of grating stimuli which either varied randomly in their orientations or rotated predictably with occasional transitions to an unexpected orientation. For single neurons and the population, there was significant enhancement in the gain of orientation-selective responses to unexpected gratings. This gain-enhancement for unexpected stimuli was prominent in both awake and anaesthetised mice. We implemented a computational model to demonstrate how trial-to-trial variability in neuronal responses were best characterised when adaptation and expectation effects were combined.

Adaptation to prevailing stimuli is a ubiquitous property of the visual system that optimizes its dynamic range. The perceived difference in orientation of successively presented lines of similar orientation is exaggerated and the perceived shape of an object is influenced by previously experienced shapes. Change in perceived shape is assumed to arise through the adaptation of shape detectors. Here we consider an alternative: adaptation within a substrate of local oriented line detectors resulting in enhanced shape contrast in similar shapes. We show that the perceived shapes of a spatially coincident circle and Cartesian grid can be manipulated independently by adaptation to geometrically transformed copies of themselves. The same transformation was applied to the circle and the grid to create the adaptors; therefore, the specificity of the effects of adaptation demonstrates that the visual system adapts to the shape of objects rather than applying transformations to the reference frame of the visual field. The tilt aftereffect predicts local changes in perceived orientation, and fields of such local effects can often account for the global change in perceived shape of complex objects, including faces.

Radial frequency (RF) patterns, paths deformed from circular by a sinusoidal modulation of radius, have proved valuable stimuli for investigation of visual shape processing. Their utility relies upon evidence that thresholds for detection of modulation decrease, as cycles of modulation are added, at a rate that cannot be accounted for by the improving probability of detection of any single cycle (probability summation). This has been interpreted as indicative of global processing. Recently Mullen, Beaudot, and Ivanov (2011), using low contrast RF patterns viewed in cosine phase through a Gaussian window, demonstrated the existence of a local cue to modulation that was more salient than the global shape cue present in sectors of RF patterns. The experiments reported here investigate why this cue has not previously obscured global integration of shape information in RF patterns. Using stimuli modulated in sine phase, Experiment 1 showed that the presence of a circular sector of path, used to complete a partially modulated RF pattern, does not raise thresholds, contrary to the suggestion of Mullen et al. (2011). Experiment 2 demonstrated integration for high and low contrast RF patterns viewed in sine phase through a Gaussian window and Experiment 3 showed the same for patterns in cosine phase if the use of a local phase specific curvature cue was precluded. Effective use of local curvature in the test comparison, then, requires knowledge of pattern orientation to define the sign of curvature. Experiment 4 demonstrated global processing of shape information for a range of radial frequencies and also showed that the local maximum gradient with respect to circular within an RF pattern covaries with threshold. This implies that it is this cue, or one that covaries linearly with it, that is integrated across cycles of modulation by the global processing mechanism.