Duration-Dependent fMRI Adaptation and Distributed Viewer-Centered Face Representation in Human Visual Cortex

Fang Fang, Scott O. Murray, Sheng He
Cerebral Cortex June 2007;17:1402--1411 doi:10.1093/cercor/bhl053

Two functional magnetic resonance imaging (fMRI) face viewpoint
adaptation experiments were conducted to investigate whether
fMRI adaptation in high-level visual cortex depends on the duration
of adaptation and how different views of a face are represented in
the human visual system. We found adaptation effects in multiple
face-selective areas, which suggest a distributed, viewer-centered
representation of faces in the human visual system. However, the
nature of the adaptation effects was dependent on the length of adaptation.
With long adaptation durations, face-selective areas along
the hierarchy of the visual system gradually exhibited viewpointtuned
adaptation. As the angular difference between the adapter
and test stimulus increased, the blood oxygen level--dependent
(BOLD) signal evoked by the test stimulus gradually increased as
a function of the amount of 3-dimensional (3D) rotation. With short
adaptation durations, however, face-selective areas in the ventral
pathway, including the lateral occipital cortex and right fusiform
area, exhibited viewpoint-sensitive adaptation. These areas showed
an increase in the BOLD signal with a 3D rotation, but this signal
increase was independent of the amount of rotation. Further, the
right superior temporal sulcus showed little or very weak viewpoint
adaptation with short adaptation durations. Our findings suggest
that long- and short-term fMRI adaptations may reflect selective
properties of different neuronal mechanisms.

The Cortical Representation of Objects Rotating in Depth

Sarah Weigelt, Zoe Kourtzi, Axel Kohler, Wolf Singer, Lars Muckli
The Journal of Neuroscience, April 4, 2007, 27(14):3864-3874;

The perception of motion provides valuable interpolations of the visual scene. This fundamental capacity of the visual system is evident in apparent rotation: by presenting only two images of an object rotated in space, a vivid illusion of a smooth apparent motion in three dimensions can be induced. The unseen interpolated rotation views are filled in by the visual system. In the present study, we identified the cortical network responsible for this filling-in process. We argue that cross talk between areas of the ventral and dorsal visual pathways promote the illusion of smooth apparent rotation. Most interestingly, the network represents the unseen object views. Using functional magnetic resonance adaptation, we are able to show that the cortical network selectively adapts to the illusory object views. Our findings provide strong evidence for cortical representations of three-dimensional rotating objects that are view invariant with respect to the rotation path. Furthermore, our results confirm psychophysical investigations that unseen interpolated rotation views can be primed by apparent motion. By applying functional magnetic resonance adaptation, we show for the first time cortical adaptation to unseen objects. Together, our neuroimaging study advances the understanding of the cortical mechanisms mediating the influence of motion on object processing.

Orientation-Selective Adaptation to Illusory Contours in Human Visual Cortex

Leila Montaser-Kouhsari, Michael S. Landy, David J. Heeger, Jonas Larsson
The Journal of Neuroscience, February 28, 2007, 27(9):2186-2195; doi:10.1523/JNEUROSCI.4173-06.2007

Humans can perceive illusory or subjective contours in the absence of any real physical boundaries. We used an adaptation protocol to look for orientation-selective neural responses to illusory contours defined by phase-shifted abutting line gratings in the human visual cortex. We measured functional magnetic resonance imaging (fMRI) responses to illusory-contour test stimuli after adapting to an illusory-contour adapter stimulus that was oriented parallel or orthogonal to the test stimulus. We found orientation-selective adaptation to illusory contours in early (V1 and V2) and higher-tier visual areas (V3, hV4, VO1, V3A/B, V7, LO1, and LO2). That is, fMRI responses were smaller for test stimuli parallel to the adapter than for test stimuli orthogonal to the adapter. In two control experiments using spatially jittered and phase-randomized stimuli, we demonstrated that this adaptation was not just in response to differences in the distribution of spectral power in the stimuli. Orientation-selective adaptation to illusory contours increased from early to higher-tier visual areas. Thus, both early and higher-tier visual areas contain neurons selective for the orientation of this type of illusory contour.

Fulltext: http://www.jneurosci.org/cgi/reprint/27/9/2186