Modulating Foveal Representation can Influence Visual Discrimination in the Periphery

A previous study by Williams et al. (2008) provided evidence for a novel form of feedback in the visual system, whereby peripheral information is contained in foveal retinotopic cortex. Beyond its possible implication for peripheral object recognition, few studies have examined the effect of a direct behavioral manipulation of the foveal feedback representation. To address this question, we measured participants\u27 peripheral visual discrimination performance while modulating their foveal representation in a series of psychophysical experiments. On each trial, participants discriminated the identities of briefly presented novel, three-dimensional objects or the orientations of gratings in a peripheral location while fixating at the center. Besides the peripheral target, another stimulus (foil) was also presented and masked at the fovea. Our results showed that for objects, when the foveal foil that was identical to the peripheral target was presented 150 ms after the onset of the peripheral target, visual discrimination of the peripheral target was improved. This congruency effect occurred even though participants did not consciously perceive the foveal stimulus. No such effect was observed when the foveal foil was presented simultaneously with the peripheral target, or when the foil was presented in a parafoveal location. The foil effect in gratings was different from that in objects in terms of its effective timing and foveal specificity, suggesting that foveal feedback may be specific to high-level objects. These results indicate that modulating foveal information can affect individuals\u27 ability to discriminate peripheral objects, suggesting a functional role of foveal representations in peripheral visual perception

Color Updating on the Apparent Motion Path

When a static stimulus appears successively at two distant locations, we perceive illusory motion of the stimulus across them–long-range apparent motion (AM). Previous studies have shown that when the apparent motion stimuli differ in shape, interpolation between the two shapes is perceived across the AM path. In contrast, the perceived color during AM has been shown to abruptly change from the color of the first stimulus into that of the second, suggesting interpolation does not occur for color during AM. Here, we report the first evidence to our knowledge, that an interpolated color, distinct from the colors of either apparent motion stimulus, is represented as the intermediate percept on the path of apparent motion. Using carefully chosen target colors—cyan, pink, and lime—that are perceptually and neurally intermediate between blue and green, orange and magenta, and green and orange respectively, we show that detection of a target presented on the apparent motion path was impaired when the color of the target was “in-between” the initial and terminal stimulus colors. Furthermore, we show that this feature-specific masking effect for the intermediate color cannot be accounted for by color similarity between the intermediate color and the color of the terminal inducer. Our findings demonstrate that intermediate colors can be interpolated over the apparent motion trajectory as in the case of shape, possibly involving similar interpolation processes for shape and color during apparent motion

Backward Position Shift in Apparent Motion

We investigated the perceived position of visual targets in apparent motion. A disc moved horizontally through three positions from -10° to +10° in the far periphery (20° above fixation), generating a compelling impression of apparent motion. In the first experiment, observers compared the position of the middle of the three discs to a subsequently presented reference. Unexpectedly, observers judged its position to be shifted backward, in the direction opposite that of the motion. We then tested the middle disc in sequences of 3, 5, and 7 discs, each covering the same spatial and temporal extents (similar speeds). The backwards shift was only found for the three-disc sequence. With the extra discs approaching more continuous motion, the perceived shift was in the same direction as the apparent motion. Finally, using a localization task with constant static references, we measured the position shifts of all the disc locations for two-disc, three-disc and four-disc apparent motion sequences. The backward shift was found for the second location of all sequences. We suggest that the backward shift of the second element along an apparent motion path is due to an attraction effect induced by the initial point of the motion

Reconstructing Representations of Dynamic Visual Objects in Early Visual Cortex

As raw sensory data are partial, our visual system extensively fills in missing details, creating enriched percepts based on incomplete bottom-up information. Despite evidence for internally generated representations at early stages of cortical processing, it is not known whether these representations include missing information of dynamically transforming objects. Long-range apparent motion (AM) provides a unique test case because objects in AM can undergo changes both in position and in features. Using fMRI and encoding methods, we found that the “intermediate” orientation of an apparently rotating grating, never presented in the retinal input but interpolated during AM, is reconstructed in population-level, feature-selective tuning responses in the region of early visual cortex (V1) that corresponds to the retinotopic location of the AM path. This neural representation is absent when AM inducers are presented simultaneously and when AM is visually imagined. Our results demonstrate dynamic filling-in in V1 for object features that are interpolated during kinetic transformations

Backward position shift in apparent motion

We investigated the perceived position of visual targets in apparent motion. A disc moved horizontally through three positions from À108 to þ108 in the far periphery (208 above fixation), generating a compelling impression of apparent motion. In the first experiment, observers compared the position of the middle of the three discs to a subsequently presented reference. Unexpectedly, observers judged its position to be shifted backward, in the direction opposite that of the motion. We then tested the middle disc in sequences of 3, 5, and 7 discs, each covering the same spatial and temporal extents (similar speeds). The backwards shift was only found for the three-disc sequence. With the extra discs approaching more continuous motion, the perceived shift was in the same direction as the apparent motion. Finally, using a localization task with constant static references, we measured the position shifts of all the disc locations for two-disc, three-disc and four-disc apparent motion sequences. The backward shift was found for the second location of all sequences. We suggest that the backward shift of the second element along an apparent motion path is due to an attraction effect induced by the initial point of the motion

Chronic Expanding Hematoma of the Thorax

We report the first case in Korea of a chronic expanding hematoma, which presented as a huge mass in the pleural cavity. A 67-year-old woman exhibiting a slowly-expanding intrathoracic mass, as revealed by a chest radiograph, was admitted to our hospital. The patient had undergone a pneumonectomy 37 years earlier during treatment for pulmonary tuberculosis. Computed tomography revealed a huge mass in her right hemithorax. The differential diagnosis of this mass included chronic empyema combined with a malignancy, such as lymphoma or a soft tissue sarcoma. The tumor, which was classified as an encapsulated chronic hematoma, was removed surgically. Samples sent for histopathological and microbiological analysis revealed no evidence of neoplasia or infection. The patient was finally diagnosed with a chronic expanding hematoma of the thorax. This case is particularly rare due to the patient's development of a very large mass after undergoing treatment for tuberculosis more than 30 years earlier

S6-2: Neural Representation in the Apparent Motion Path

When a static stimulus appears successively at two different locations, we perceive a transition of the stimulus across them—apparent motion. Previous studies have shown that some spatio-temporal representation is reconstructed in the apparent motion path and it leads to increased activation in the region of the primary visual cortex (V1) corresponding to the apparent motion path (Muckli et al., 2005 PLoS Biology 3 1501–1510). However, little is known about whether visual properties of an object engaged in apparent motion are maintained in this representation. In order to address this question, we used fMRI and pattern classification methods to examine the neural representation created on the apparent motion path when the object changes its orientation across the apparent motion path. Two intermediate orientations (0° and 90°) on the apparent motion path were induced by presenting gratings with different orientations at separate locations. The gratings were presented in a bistable quartet sequence, and subjects were instructed to perceive either vertical or horizontal direction of motion during each trial. The results show that the regions of V1 contain information of the intermediate representations (0° vs. 90°) between the two gratings when they correspond to the path of perceived rotation but not when they are no longer on the motion path. This suggests that V1 generates neural representation of visual features that do not exist in the physical stimulus, but that correspond to our conscious perceptual experience of dynamic visual objects

Modulating foveal representation can influence visual discrimination in the periphery

A previous study by Williams et al. (2008) provided evidence for a novel form of feedback in the visual system, whereby peripheral information is contained in foveal retinotopic cortex. Beyond its possible implication for peripheral object recognition, few studies have examined the effect of a direct behavioral manipulation of the foveal feedback representation. To address this question, we measured participants' peripheral visual discrimination performance while modulating their foveal representation in a series of psychophysical experiments. On each trial, participants discriminated the identities of briefly presented novel, three-dimensional objects or the orientations of gratings in a peripheral location while fixating at the center. Besides the peripheral target, another stimulus (foil) was also presented and masked at the fovea. Our results showed that for objects, when the foveal foil that was identical to the peripheral target was presented 150 ms after the onset of the peripheral target, visual discrimination of the peripheral target was improved. This congruency effect occurred even though participants did not consciously perceive the foveal stimulus. No such effect was observed when the foveal foil was presented simultaneously with the peripheral target, or when the foil was presented in a parafoveal location. The foil effect in gratings was different from that in objects in terms of its effective timing and foveal specificity, suggesting that foveal feedback may be specific to high-level objects. These results indicate that modulating foveal information can affect individuals' ability to discriminate peripheral objects, suggesting a functional role of foveal representations in peripheral visual perception.1431sciescopu