Dataset Information

FMRI reveals that non-local processing in ventral retinotopic cortex underlies perceptual grouping by temporal synchrony.

ABSTRACT:

Unlabelled

When spatially separated objects appear and disappear in a synchronous manner, they perceptually group into a single global object that itself appears and disappears. We employed functional magnetic resonance imaging (fMRI) to identify brain regions involved in this type of perceptual grouping. Subjects viewed four chromatically-defined disks (one per visual quadrant) that flashed on and off. We contrasted %BOLD signal changes between blocks of synchronously flashing disks (Grouping) with blocks of asynchronously flashing disks (no-Grouping).

Results

A region of interest analysis revealed %BOLD signal change in the Grouping condition was significantly greater than in the no-Grouping condition within retinotopic areas V2, V3, and V4v. Within a single quadrant of the visual field, the spatio-temporal information present in the image was identical across the two stimulus conditions. As such, the two conditions could not be distinguished from each other on the basis of the rate or pattern of flashing within a single visual quadrant. The observed results must therefore arise through nonlocal interactions between or within these retinotopic areas, or arise from outside these retinotopic areas. Furthermore, when V2 and V3 were split into ventral and dorsal sub-ROIs, ventral retinotopic areas V2v and V3v preferentially differentiated between the two conditions whereas the corresponding dorsal areas V2d and V3d did not. In contrast, within hMT+, %BOLD signal was significantly greater in the no-Grouping condition.

Conclusion

Nonlocal processing within, between, or to ventral retinotopic cortex at least as early as V2v, and including V3v, and V4v, underlies perceptual grouping via temporal synchrony.

SUBMITTER: Caplovitz GP

PROVIDER: S-EPMC6871124 | biostudies-literature | 2008 Jun

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

fMRI reveals that non-local processing in ventral retinotopic cortex underlies perceptual grouping by temporal synchrony.

Caplovitz Gideon P GP Barroso Diego J DJ Hsieh Po-Jang PJ Tse Peter U PU

Human brain mapping 20080601 6

<h4>Unlabelled</h4>When spatially separated objects appear and disappear in a synchronous manner, they perceptually group into a single global object that itself appears and disappears. We employed functional magnetic resonance imaging (fMRI) to identify brain regions involved in this type of perceptual grouping. Subjects viewed four chromatically-defined disks (one per visual quadrant) that flashed on and off. We contrasted %BOLD signal changes between blocks of synchronously flashing disks (Gr ...[more]

PMID: 17598165

Similar Datasets

Project description:Immediate serial spatial recall measures the ability to retain sequences of locations in short-term memory and is considered the spatial equivalent of digit span. It is tested by requiring participants to reproduce sequences of movements performed by an experimenter or displayed on a monitor. Different organizational factors dramatically affect serial spatial recall but they are often confounded or underspecified. Untangling them is crucial for the characterization of working-memory models and for establishing the contribution of structure and memory capacity to spatial span. We report five experiments assessing the relative role and independence of factors that have been reported in the literature. Experiment 1 disentangled the effects of spatial clustering and path-length by manipulating the distance of items displayed on a touchscreen monitor. Long-path sequences segregated by spatial clusters were compared with short-path sequences not segregated by clusters. Recall was more accurate for sequences segregated by clusters independently from path-length. Experiment 2 featured conditions where temporal pauses were introduced between or within cluster boundaries during the presentation of sequences with the same paths. Thus, the temporal structure of the sequences was either consistent or inconsistent with a hierarchical representation based on segmentation by spatial clusters but the effect of structure could not be confounded with effects of path-characteristics. Pauses at cluster boundaries yielded more accurate recall, as predicted by a hierarchical model. In Experiment 3, the systematic manipulation of sequence structure, path-length, and presence of path-crossings of sequences showed that structure explained most of the variance, followed by the presence/absence of path-crossings, and path-length. Experiments 4 and 5 replicated the results of the previous experiments in immersive virtual reality navigation tasks where the viewpoint of the observer changed dynamically during encoding and recall. This suggested that the effects of structure in spatial span are not dependent on perceptual grouping processes induced by the aerial view of the stimulus array typically afforded by spatial recall tasks. These results demonstrate the independence of coding strategies based on structure from effects of path characteristics and perceptual grouping in immediate serial spatial recall.

Project description:Primates have specialized domains in inferior temporal (IT) cortex that are responsive to particular image categories. Though IT traditionally has been regarded as lacking retinotopy, several recent studies in monkeys have shown that retinotopic maps extend to face patches along the lower bank of the superior temporal sulcus (STS) and neighboring regions of IT cortex. Here, we used fMRI to map the retinotopic organization of medial ventral temporal cortex in four monkeys (2 male and 2 female). We confirm the presence of visual field maps within and around the lower bank of the STS and extend these prior findings to scene-selective cortex in the ventral-most regions of IT. Within the occipitotemporal sulcus (OTS), we identified two retinotopic areas, OTS1 and OTS2. The polar angle representation of OTS2 was a mirror reversal of the OTS1 representation. These regions contained representations of the contralateral periphery and were selectively active for scene versus face, body, or object images. The extent of this retinotopy parallels that in humans and shows that the organization of the scene network is preserved across primate species. In addition retinotopic maps were identified in dorsal extrastriate, posterior parietal, and frontal cortex as well as the thalamus, including both the lateral geniculate nucleus and pulvinar. Together, it appears that most, if not all, of the macaque visual system contains organized representations of visual space.SIGNIFICANCE STATEMENT Primates have specialized domains in inferior temporal (IT) cortex that are responsive to particular image categories. Though retinotopic maps are considered a fundamental organizing principle of posterior visual cortex, IT traditionally has been regarded as lacking retinotopy. Recent imaging studies have demonstrated the presence of several visual field maps within the lateral IT. Using neuroimaging, we found multiple representations of visual space within ventral IT cortex of macaques that included scene-selective cortex. Scene domains were biased toward the peripheral visual field. These data demonstrate the prevalence of visual field maps throughout the primate visual system, including late stages in the ventral visual hierarchy, and support the idea that domains representing different categories are biased toward different parts of the visual field.