Mark D. Lescroart

Adaptation in the fusiform face area (FFA): Image or person?

Viewing a sequence of faces of two different people results in a greater Blood Oxygenation Level Dependent (BOLD) response in FFA compared to a sequence of identical faces. Changes in identity, however, necessarily involve changes in the image. Is the release from adaptation a result of a change in face identity, per se, or could it be an effect that would arise from any change in the image of a face? Subjects viewed a sequence of two faces that could be of the same or different person, and in the same or different orientation in depth. Critically, the physical similarity of view changes of the same person was scaled, by Gabor-jet differences, to be equivalent to that produced by an identity change. Both person and orientation changes produced equivalent releases from adaptation in FFA (relative to identical faces) suggesting that FFA is sensitive to the physical similarity of faces rather than to the individuals depicted in the images.

Adaptation to objects in the lateral occipital complex (LOC): Shape or semantics?

A change in the basic-level class when viewing a sequence of two objects produces a large release from adaptation in LOC compared to when the images are identical. Is this due to a change in semantics or shape? In an fMRI-adaptation experiment, subjects viewed a sequence of two objects and judged whether the stimuli were identical in shape. Different-shaped stimuli could be from the same or different basic-level classes, where the physical similarities of the pairs in the two conditions were equated by a model of simple cell similarity. BOLD responses in LOC for the two conditions were equivalent, and higher than that of the identical condition, indicating that LOC is sensitive to shape rather than to basic-level semantics.

A cross-cultural study of the representation of shape: Sensitivity to generalized cone dimensions

Many of the phenomena underlying shape recognition can be derived from an assumption that the representation of simple parts can be understood in terms of independent dimensions of generalized cones, e.g., whether the axis of a cylinder is straight or curved or whether the sides are parallel or nonparallel. What enables this sensitivity? One explanation is that the representations derive from our immersion in a manufactured world of simple objects, e.g., a cylinder and a funnel, where these dimensions can be readily discerned independent of other stimulus variations. An alternative explanation is that genetic coding and/or early experience with extended contours—a characteristic of all naturally varying visual worlds—would be sufficient to develop the appropriate representations. The Himba, a seminomadic people in a remote region of Northwestern Namibia with little exposure to regular, simple artifacts, were virtually identical to western observers in representing generalized-cone dimensions of simple shapes independently. Thus immersion in a world of simple, manufactured shapes is not required for the development of a representation that specifies these dimensions independently.

A Cross-cultural test of the independence of the representation of generalized-cone dimensions

• Even though the results in the “Regular” condition could be attributed to low-level features, the results in the “Noisy” condition could not • Since both “Noisy” and “Regular” runs showed the same pattern, we conclude that the same mechanism is at work in both • Humans are independently sensitive to dimensions of generalized cones, even after growing up in markedly different visual environments “Noisy” “Regular” • Subjects had to divide the display into two groups • Feedback was given after each trial in the form of a green line over the correct divide • “Noisy” displays were shown in dfifferent sessions to some subjects Experimental Task: texture segregation

The neural representation of spatial relationships by anatomical binding

Many theorists have hypothesized that when viewing a multi-object scene, the visual system assigns each object’s bundled features to separate ‘slots’. Such dynamic “binding” to multiple slots is at the heart of the Object Files theory (Kahneman, Treisman, & Gibbs 1992), Visual Short-Term Memory (VSTM) models, FINST theory (Pylyshyn 1989), Recognition-by-Components theory (Biederman 1987) and others.

Evidence for object file encoding in the posterior Fusiform Gyrus (pFs) and the Intraparietal Sulcus (IPS)

Large change in representation: Introduction: Many theorists have hypothesized that when viewing a multi-object scene, the visual system assigns each object’s bundled features to separate ‘slots’. Such dynamic “binding” to multiple slots is at the heart of the Object Files theory (Kahneman, Treisman, & Gibbs 1992), Visual Short-Term Memory (VSTM) models, FINST theory (Pylyshyn 1989), Recognition-by-Components theory (Biederman 1987) and others. Such a slot-based representation is potentially very powerful because relation information can be explicitly associated with each slot, i.e., ‘this slot contains the top object’s features’, allowing for true understanding of visual structure. In contrast, certain scene manipulations will produce a disproportionately large change in neural representation: A B