1,721,084 research outputs found
Motion Integration over Space: Interaction of the Center and Surround Motion**This research was first reported at the Annual Meeting of the Association for Research in Vision and Ophthalmology, May 1994 and 1995.
No full textAbstractMotion integration occurs over a restricted range of visual space. However, there have been studies suggesting interactions among motion detectors operating on widely separated spatial regions. To understand these lateral spatial interactions beyond motion pooling regions, we examined the effect of surrounding motion on the direction of the center stimulus under several stimulus conditions. We have found that there is a motion direction shift of the center stimulus caused by surrounding motion depending on its motion direction, spatial proximity to the center stimulus, contrast, speed, and the extent of motion area. This effect was observed both for monocular and dichoptic presentations of the pattern. However, the perceived direction shift decreased when the spatial frequency ratio of the center and surround stimuli varied, or a non-Fourier motion pattern was used for both center and surround stimuli. We present a model consisting of lateral inhibitory interactions between pattern motion unit networks to explain the direction shift observed in the experiments. © 1997 Elsevier Science Ltd. All rights reserved
Direction repulsion between components in motion transparency
No full textAbstractWe measured the perceived direction of one motion component as a function of the contrast and speed of a second component for three pattern classes: plaids with two different spatial frequency components, multi-aperture patterns, and contrast-modulated (CM) patterns. The components were moving at ±63.4 or ±71.6 deg to the vertical, angles where motion transparency always occurred under our conditions. For multi-aperture and CM patterns on a single spatial scale, the components were perceived to deviate from the component motion directions by up to 20 deg at high contrasts or high speeds of the second component. However, for plaids with components on different spatial scales, the test components were perceived moving in the component directions regardless of the contrast or the speed of the second component. Our data show that this direction repulsion between components occurs within a single spatial scale but not between widely separated spatial scales. This implies that two different mechanisms are involved in motion transparency
Discrimination of familiar and unfamiliar synthetic faces by North Americans and Koreans
No full textA new class of synthetic-face stimuli has been recently introduced for studying visual face processing. Synthetic faces are extracted from digital photographs of individual faces and bandpass-filtered after converting into radial frequencies for the head shape. In face-discrimination experiments Wilson et al (2002, submitted), using synthetic-face cubes, found that discrimination thresholds for highly distinctive face cubes centred on a non-mean face were 1.45 times higher than for faces centred on the mean face. These results might give us a quantitative insight into 'the other-race effect'. To investigate further this problem, we measured the face-discrimination thresholds for non-North-American faces, in this case Korean faces with Korean subjects. We found that the increment thresholds for mean face cubes for three subjects averaged 4.4% in front view and 5.6% in side view. However, the thresholds rose to 6.1% and 7.8% for non-mean front and side face cubes, respectively. In good agreement with the previous study, these results indicate that we do have finer discrimination ability for familiar faces than for unfamiliar faces. We will switch North-American and Korean faces and test each with the other group to get a quantitative measure of the 'other-race effect'
Recognition memory for Caucasian and Korean synthetic faces
No full textSynthetic faces were generated by digitising 37 points on individual face photographs. Using both Caucasian and Korean synthetic faces, we designed an experiment to determine whether there was any memory difference between the two face categories defined only by face geometry and not by skin colour, hair texture, etc. In each experiment, observers first studied four Caucasian and four Korean faces presented in random order. Following this, there was a 15 min rest period before the recognition experiment began. On each recognition trial, one previously studied face was paired with three distractor faces in a spatial 4AFC procedure. Importantly, the distractor faces were all chosen to be orthogonal to one another and to lie a fixed geometric distance from the studied face. Overall recognition memory was 51% correct, far above the chance value of 25%. Recognition memory for Caucasian faces (59%) was significantly greater than for Korean faces (44%), even though observers were never told that the faces comprised two ethnic categories. We conclude that recognition memory for synthetic faces exhibits implicit categorisation effects for the geometry of Caucasian and Korean faces
Dynamics of a divisive gain control in human vision1Portions of this research were first reported at the ARVO annual meeting in 1990.1
No full textAbstractEvidence for a divisive contrast gain control in human vision was obtained using a contrast version of the probe-on-flash technique that has been employed in the light adaptation literature. Thresholds were measured for a briefly flashed (30 ms), vertical test pattern superimposed on a cosine mask as a function of time after mask onset (SOA). Threshold elevations declined monotonically for SOAs up to 150 ms. and exhibited an exponential time course with an average time constant of 51 ms. Increment thresholds for the test as a function of mask contrast provide direct evidence that these effects are due to operation of a divisive gain control within the first 150 ms after stimulus onset. Experiments to measure the spatial spread of this gain control show it to be localized to a region of no more than 45 arc min radius
Neuronal correlates of binocular rivalry in second-order patterns
No full textIt has been recently reported that there is binocular rivalry in second-order patterns with a dynamic carrier [Kim et al, 2006 Journal of Vision 6(6), VSS 07, abstract 47a]. To find neuronal correlates of second-order binocular rivalry, we measured BOLD signal changes in early visual cortex while subjects viewed uncorrelated dynamic random-dot fields whose contrasts were modulated at 1.5 cycles deg-1 sine-wave with orientation of ±45°. Subjects were required to press either right or left button for alternating percepts tilted rightward or leftward, respectively. We found that there is no difference of V1 activity in both hemispheres when either right or left response was made. However, there was a fluctuation of activity in V2 for alternating percepts. V2 activity increased with the right response and decreased with the left response in the left hemisphere, while the activity pattern was reversed in the right hemisphere. These results indicate that V2 area is a special site for second-order binocular processing as suggested in form and motion vision
Hysteresis effects in stereopsis and binocular rivalry
No full textAbstractNeural hysteresis plays a fundamental role in stereopsis and reveals the existence of positive feedback at the cortical level [Wilson, H. R., & Cowan, J. D. (1973). A mathematical theory of the functional dynamics of cortical and thalamic nervous tissue. Kybernetik 13(2), 55–80]. We measured hysteresis as a function of orientation disparity in tilted gratings in which a transition is perceived between stereopsis and binocular rivalry. The patterns consisted of sinusoidal gratings with orientation disparities (0°, 1°, 2°, …, 40°) resulting in various degrees of tilt. A movie of these 41 pattern pairs was shown at a rate of 0.5, 1 or 2 pattern pairs per second, in forward or reverse order. Two transition points were measured: the point at which the single tilted grating appeared to split into two rivalrous gratings (T1), and the point at which two rivalrous gratings appeared to merge into a single tilted grating (T2). The transitions occurred at different orientation disparities (T1=25.4°, T2=17.0°) which was consistent with hysteresis and far exceeded the difference which could be attributed to reaction time. The results are consistent with a cortical model which includes positive feedback and recurrent inhibition between neural units representing different eyes and orientations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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