Anterior Regions of Monkey Parietal Cortex Process Visual 3D Shape

147

203

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.

Section: Classification Of Depth Position For Correlated and Anticorrmentioning

confidence: 95%

Multivoxel Pattern Selectivity for Perceptually Relevant Binocular Disparities in the Human Brain

Preston¹,

Li²,

Kourtzi³

et al. 2008

147

203

“…Since the TEs and AIP neurons are also selective for 2D shape in frontoparallel planes, they carry all the information needed to represent 3D shape from stereo. Using fMRI in the awake monkey we showed that these two regions are sensitive to the interaction between surface order and disparity, responding more to binocular curved 3D surfaces than to binocular flat surfaces at different depths, relative to their respective monocular controls (Durand et al, 2007;Joly et al, 2007). We thus have a MR signature for second-order disparityselective neurons and the aim of the present experiments is to use this signature in human subjects to chart the regions of the human brain that may house similar neurons.…”

Section: Introductionmentioning

confidence: 97%

“…It is worth pointing out that in the monkey we also have an MR signature for first order selective neurons (Durand et al, 2007), but this was not used in the present experiments.…”

Section: Introductionmentioning

confidence: 99%

The Processing of Three-Dimensional Shape from Disparity in the Human Brain

Georgieva¹,

Peeters²,

Kolster³

et al. 2009

192

233

Three-dimensional (3D) shape is important for the visual control of grasping and manipulation and for object recognition. Although there has been some progress in our understanding of how 3D shape is extracted from motion and other monocular cues, little is known of how the human brain extracts 3D shape from disparity, commonly regarded as the strongest depth cue. Previous fMRI studies in the awake monkey have established that the interaction between stereo (present or absent) and the order of disparity (

“…Visual areas in the PPC in humans and monkeys exhibit selectivity for three-dimensional cues of shape such as structurefrom-motion (SFM) (Vanduffel et al, 2002), stereopsis, and perspective (Shikata et al, 1996(Shikata et al, , 2001(Shikata et al, , 2003Sugihara et al, 2002;Anderson and Siegel, 2005;Orban et al, 2006;Durand et al, 2007). Some of the three-dimensional cue-selective neurons in these regions exhibit properties that are suggestive of a role in "high-level" visual perception.…”

Section: Introductionmentioning

confidence: 99%

Dorsal–Ventral Integration in the Recognition of Motion-Defined Unfamiliar Faces

Farivar¹,

Blanke²,

Chaudhuri³

2009

The primate visual system is organized into two parallel anatomical pathways, both originating in early visual areas but terminating in posterior parietal or inferior temporal regions. Classically, these two pathways have been thought to subserve spatial vision and visual guided actions (dorsal pathway) and object identification (ventral pathway). However, evidence is accumulating that dorsal visual areas may also represent many aspects of object shape in absence of demands for attention or action. Dorsal visual areas exhibit selectivity for three-dimensional cues of depth and are considered necessary for the extraction of surfaces from depth cues and can carry out cognitive functions with such cues as well. These results suggest that dorsal visual areas may participate in object recognition, but it is unclear to what capacity. Here, we tested whether three-dimensional structure-from-motion (SFM) cues, thought to be computed exclusively by dorsal stream mechanisms, are sufficient to drive complex object recognition. We then tested whether recognition of such stimuli relies on dorsal stream mechanisms alone, or whether dorsal-ventral integration is invoked. Results suggest that such cues are sufficient to drive unfamiliar face recognition in normal participants and that ventral stream areas are necessary for both identification and learning of unfamiliar faces from SFM cues.