The lateral occipital complex subserves the perceptual persistence of motion-defined groupings.

How are the bits and pieces of retinal information assembled and integrated to form the coherent objects that we see? One long-established principle is that elements that move as a group are linked together. For instance a fragmented line-drawing of an object, placed on a background of randomly distributed short lines, can be impossible to see. But if the object moves relative to the background, its shape is instantly recognized. Even after the motion stops, the percept of the object persists briefly before it fades into the background of random lines. Where in the brain does the percept of the object persist? Using functional brain imaging, we found that such moving line-drawings activated both motion-sensitive areas (medial temporal complex, MT+) and object-sensitive areas (lateral occipital complex, LOC). However, after the motion stopped only the LOC maintained its activity while the percept endured. Evidently a percept assembled by motion-sensitive areas like MT+ can be stored, at least briefly, in the LOC

A contralateral preference in the lateral occipital area: sensory and attentional mechanisms.

Here we examined the level of the lateral occipital (LO) area within the processing stream of the ventral visual cortex. An important determinant of an area\u27s level of processing is whether it codes visual elements on both sides of the visual field, as do higher visual areas, or prefers those in the contralateral visual field, as do early visual areas. The former would suggest that LO, on one side, combines bilateral visual elements into a whole, while the latter suggests that it codes only the parts of forms. We showed that LO has a relative preference for visual objects in the contralateral visual field. LO responses were influenced by attention. However, relative changes in LO activity caused by changes in object location were preserved even when attention was shifted away from the objects to moving random dot patterns on the opposite side. Our data offer a new view on LO as an intermediate, but not a high-level, visual area in which neurons are driven by visual input and spatial attention in a multiplicative fashion

Human parietal reach region primarily encodes intrinsic visual direction, not extrinsic movement direction, in a visual motor dissociation task.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gaze-centered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and event-related functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual-motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world- or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates

Brief Communication Gaze-Centered Updating of Visual Space in Human Parietal Cortex

Single-unit recordings have identified a region in the posterior parietal cortex (PPC) of the monkey that represents and updates visual space in a gaze-centered frame. Here, using event-related functional magnetic resonance imaging, we identified an analogous bilateral region in the human PPC that shows contralateral topography for memory-guided eye movements and arm movements. Furthermore, when eye movements reversed the remembered horizontal target location relative to the gaze fixation point, this PPC region exchanged activity across the two cortical lobules. This shows that the human PPC dynamically updates the spatial goals for action in a gaze-centered frame

Face Inversion Reduces the Persistence of Global Form and Its Neural Correlates

Face inversion produces a detrimental effect on face recognition. The extent to which the inversion of faces and other kinds of objects influences the perceptual binding of visual information into global forms is not known. We used a behavioral method and functional MRI (fMRI) to measure the effect of face inversion on visual persistence, a type of perceptual memory that reflects sustained awareness of global form. We found that upright faces persisted longer than inverted versions of the same images; we observed a similar effect of inversion on the persistence of animal stimuli. This effect of inversion on persistence was evident in sustained fMRI activity throughout the ventral visual hierarchy, including the lateral occipital area (LO), two face-selective visual areas—the fusiform face area (FFA) and the occipital face area (OFA)—and several early visual areas. V1 showed the same initial fMRI activation to upright and inverted forms but this activation lasted longer for upright stimuli. The inversion effect on persistence-related fMRI activity in V1 and other retinotopic visual areas demonstrates that higher-tier visual areas influence early visual processing via feedback. This feedback effect on figure-ground processing is sensitive to the orientation of the figure

Mechanical properties of the extracellular muscles of the cat.

Static and dynamic tension variations due to different after populations in the inferior oblique eye muscle of anesthetized cats were studied during changes in length and electrical activation, and following injections of succinylcholine. Mechanical stiffness vectors for these fiber populations, obtained from their responses to small sinusoidal length change, indicated at low frequencies the presence of velocity independent friction and, at high frequencies, a phase lag or tension relative to length in the active components. Isometric tension dynamics of single motor units were found to be variable. Studies on the whole muscle confirmed non-uniform dynamics and provided new information on the relationship between isometric tension and stimulus carrier rate, stimulus modulation depth, and muscle length.Les variations statiques et dynamiques de tension dues à différentes populations de fibres dans le muscle inférieur oblique de l'oeil furent étudiées, chez des chats anesthésiés, au cours de changements de longueur du muscle et de stimulation électrique ainsi qu'après injection de succinylcholine. Les vecteurs de rigidité mécanique, (mechanical stiffness) de ces populations de fibres, obtenues d'après leur réponse a des changements de longueur sinusoidaux de petite amplitude, indiquent, aux basses fréquences, la présence d'une friction indépendante de la vitesse et, aux hautes fréquences, un retard de la tension par rapport à la longueur dans les éléments actifs. Ces études ont montré que les propriétés dynamiques de tension isométrique d'unités motrices isolées sont variables. Les résultats obtenus sur le muscle entier ont confirmé ces proprietes dynamiques non-uniformes et ont procure des informations nouvelles sur les relations entre la tension isométrique et la fréquence moyenne de stimulation électrique, l'amplitude de la modulation de cette fréquence, et la longueur musculaire