Processing of binocular disparity is thought to be widespread throughout cortex, highlighting its importance for perception and action. Yet the computations and functional roles underlying this activity across areas remain largely unknown. Here, we trace the neural representations mediating depth perception across human brain areas using multivariate analysis methods and high-resolution imaging. Presenting disparity-defined planes, we determine functional magnetic resonance imaging (fMRI) selectivity to near versus far depth positions. First, we test the perceptual relevance of this selectivity, comparing the pattern-based decoding of fMRI responses evoked by random dot stereograms that support depth perception (correlated RDS) with the decoding of stimuli containing disparities to which the perceptual system is blind (anticorrelated RDS). Preferential disparity selectivity for correlated stimuli in dorsal (visual and parietal) areas and higher ventral area LO (lateral occipital area) suggests encoding of perceptually relevant information, in contrast to early (V1, V2) and intermediate ventral (V3v, V4) visual cortical areas that show similar selectivity for both correlated and anticorrelated stimuli. Second, manipulating disparity parametrically, we show that dorsal areas encode the metric disparity structure of the viewed stimuli (i.e., disparity magnitude), whereas ventral area LO appears to represent depth position in a categorical manner (i.e., disparity sign). Our findings suggest that activity in both visual streams is commensurate with the use of disparity for depth perception but the neural computations may differ. Intriguingly, perceptually relevant responses in the dorsal stream are tuned to disparity content and emerge at a comparatively earlier stage than categorical representations for depth position in the ventral stream.

Humans exploit a range of visual depth cues to estimate three-dimensional (3D) structure. For example, the slant of a nearby tabletop can be judged by combining information from binocular disparity, texture and perspective. Behavioral tests show humans combine cues near-optimally, a feat that could depend on: (i) discriminating the outputs from cue-specific mechanisms, or (ii) fusing signals into a common representation. While fusion is computationally attractive, it poses a significant challenge, requiring the integration of quantitatively different signals. We used functional magnetic resonance imaging (fMRI) to provide evidence that dorsal visual area V3B/KO meets this challenge. Specifically, we found that fMRI responses are more discriminable when two cues (binocular disparity and relative motion) concurrently signal depth, and that information provided by one cue is diagnostic of depth indicated by the other. This suggests a cortical node important when perceiving depth, and highlights computations based on fusion in the dorsal stream.

Perceiving the three-dimensional (3D) properties of the environment relies on the brain bringing together ambiguous cues (e.g., binocular disparity, shading, texture) with information gained from short-and long-term experience. Perceptual aftereffects, in which the perception of an ambiguous 3D stimulus is biased away from the shape of a previously viewed stimulus, provide a sensitive means of probing this process, yet little is known about their neural basis. Here, we investigate 3D aftereffects using psychophysical and functional MRI (fMRI) adaptation paradigms to gain insight into the cortical circuits that mediate the perceptual interpretation of ambiguous depth signals. Using two classic bistable stimuli (Mach card, kinetic depth effect), we test aftereffects produced by 3D shapes defined by binocular (disparity) or monocular (texture, shading) depth cues. We show that the processing of ambiguous 3D stimuli in dorsal visual cortical areas (V3B/KO, V7) and posterior parietal regions is modulated by adaptation in line with perceptual aftereffects. Similar behavioral and fMRI adaptation effects for the two types of bistable stimuli suggest common neural substrates for depth aftereffects independent of the inducing depth cues (disparity, texture, shading). In line with current thinking about the role of adaptation in sensory optimization, our findings provide evidence that estimation of 3D shape in dorsal cortical areas takes account of the adaptive context to resolve depth ambiguity and interpret 3D structure.

Exploiting scene context and object– object co-occurrence is critical in guiding eye movements and facilitating visual search, yet the mediating neural mechanisms are unknown. We used functional magnetic resonance imaging while observers searched for target objects in scenes and used multivariate pattern analyses (MVPA) to show that the lateral occipital complex (LOC) can predict the coarse spatial location of observers’ expectations about the likely location of 213 different targets absent from the scenes. In addition, we found weaker but significant representations of context location in an area related to the orienting of attention (intraparietal sulcus, IPS) as well as a region related to scene processing (retrosplenial cortex, RSC). Importantly, the degree of agreement among 100 independent raters about the likely location to contain a target object in a scene correlated with LOC’s ability to predict the contextual location while weaker but significant effects were found in IPS, RSC, the human motion area, and early visual areas (V1, V3v). When contextual information was made irrelevant to observers’ behavioral task, the MVPA analysis of LOC and the other areas’ activity ceased to predict the location of context. Thus, our findings suggest that the likely locations of targets in scenes are represented in various visual areas with LOC playing a key role in contextual guidance during visual search of objects in real scenes.