查看更多>>摘要：Center-surround antagonism, as a ubiquitous feature in visual processing, usually leads to inferior perception for a large stimulus compared to a small one. For example, it is more difficult to judge the motion direction of a large high-contrast pattern than that of a small one. However, this spatial suppression in the motion dimension was only reported for luminance motion, and was not found for chromatic motion. Given that center-surround suppression only occurs for strong visual inputs, we hypothesized that previous failure in finding spatial suppression of chromatic motion might be due to weak chromatic motion being induced with stimuli of limited parameters. In this study, we used phase-shift discrimination and motion-direction discrimination tasks to measure motion spatial suppression induced by stimuli of two spatial frequencies (0.5 and 2 cpd) and two contrasts (low and high). We found that spatial suppression of the chromatic motion was stably observed for stimuli of high spatial frequency (2 cpd) and high contrast and spatial summation occurred for stimuli of low spatial frequency (0.5 cpd). Intriguingly, there was no correlations between the motion spatial suppressions of luminance motion and chromatic motion, implying that the two types of spatial suppression are not originated from the same neural processing. Our findings indicate that spatial suppression also exists for chromatic motion, and the mechanisms underlying the spatial suppression of chromatic motion is different from that of luminance motion.
查看更多>>摘要：Center-surround antagonism, as a ubiquitous feature in visual processing, usually leads to inferior perception for a large stimulus compared to a small one. For example, it is more difficult to judge the motion direction of a large high-contrast pattern than that of a small one. However, this spatial suppression in the motion dimension was only reported for luminance motion, and was not found for chromatic motion. Given that center-surround suppression only occurs for strong visual inputs, we hypothesized that previous failure in finding spatial suppression of chromatic motion might be due to weak chromatic motion being induced with stimuli of limited parameters. In this study, we used phase-shift discrimination and motion-direction discrimination tasks to measure motion spatial suppression induced by stimuli of two spatial frequencies (0.5 and 2 cpd) and two contrasts (low and high). We found that spatial suppression of the chromatic motion was stably observed for stimuli of high spatial frequency (2 cpd) and high contrast and spatial summation occurred for stimuli of low spatial frequency (0.5 cpd). Intriguingly, there was no correlations between the motion spatial suppressions of luminance motion and chromatic motion, implying that the two types of spatial suppression are not originated from the same neural processing. Our findings indicate that spatial suppression also exists for chromatic motion, and the mechanisms underlying the spatial suppression of chromatic motion is different from that of luminance motion.
查看更多>>摘要：Our results connect higher-order color mechanisms deduced from psychophysics with the known diversity of populations of double-opponent, color-responsive cells in V1. We used the chromatic visual evoked potential, the cVEP, to study responses in human visual cortex to equiluminant color patterns. Stimuli were modulated along three directions in color space: the cardinal directions, L-M and S, and along the line in color space from the white point to the color of the Red LED in the display screen (the Red direction). The Red direction is roughly intermediate between L-M and S in DKL space in cone-contrast coordinates. While cVEP response amplitude, latency, and width-and their dependences on cone contrast- were similar in the L-M and Red directions, the Transientness of the Red response was significantly greater than for responses to stimuli in the L-M direction and in the S direction. This difference in response dynamics supports the concept that there are multiple, distinct neuronal populations, so-called higher-order color mechanisms, for color perception within human V1 cortex.
查看更多>>摘要：Our results connect higher-order color mechanisms deduced from psychophysics with the known diversity of populations of double-opponent, color-responsive cells in V1. We used the chromatic visual evoked potential, the cVEP, to study responses in human visual cortex to equiluminant color patterns. Stimuli were modulated along three directions in color space: the cardinal directions, L-M and S, and along the line in color space from the white point to the color of the Red LED in the display screen (the Red direction). The Red direction is roughly intermediate between L-M and S in DKL space in cone-contrast coordinates. While cVEP response amplitude, latency, and width-and their dependences on cone contrast- were similar in the L-M and Red directions, the Transientness of the Red response was significantly greater than for responses to stimuli in the L-M direction and in the S direction. This difference in response dynamics supports the concept that there are multiple, distinct neuronal populations, so-called higher-order color mechanisms, for color perception within human V1 cortex.
Hartstein, K. C.Saleki, S.Ziman, K.Cavanagh, P....
5页
查看更多>>摘要：When one figure is replaced with another that overlaps its spatial location, observers perceive an illusory, continuous shape change of the original object, a phenomenon known as transformational apparent motion (TAM). The current study investigated the extent to which TAM depends on a common, high-level shape representation that is independent of the shape-defining attribute. Specifically, we tested whether TAM is perceived similarly for both first- and second-order objects, defined by luminance and texture contrast, respectively. A compelling motion percept was observed in second-order TAM displays that was comparable to that seen in firstorder TAM displays. Importantly, TAM for both stimulus classes showed the same pattern over a range of stimulus onset asynchronies. These results support the high-level shape account, indicating that TAM is driven by segmentation mechanisms that rely on high-level shape information rather than low-level visual characteristics.
Hartstein, K. C.Saleki, S.Ziman, K.Cavanagh, P....
5页
查看更多>>摘要：When one figure is replaced with another that overlaps its spatial location, observers perceive an illusory, continuous shape change of the original object, a phenomenon known as transformational apparent motion (TAM). The current study investigated the extent to which TAM depends on a common, high-level shape representation that is independent of the shape-defining attribute. Specifically, we tested whether TAM is perceived similarly for both first- and second-order objects, defined by luminance and texture contrast, respectively. A compelling motion percept was observed in second-order TAM displays that was comparable to that seen in firstorder TAM displays. Importantly, TAM for both stimulus classes showed the same pattern over a range of stimulus onset asynchronies. These results support the high-level shape account, indicating that TAM is driven by segmentation mechanisms that rely on high-level shape information rather than low-level visual characteristics.
Christie, JohnHilchey, Matthew D.Klein, Raymond M.
11页
查看更多>>摘要：Oculomotor research shows that eye movements are primed toward the midpoint of an array of visual stimuli, such that an eye movement to a visual target is executed most rapidly when it appears near the midpoint of an earlier array. At longer intervals between the prime and target, this facilitatory effect can reverse to become inhibitory - such that eye movements are slower when made toward the midpoint - but the source of this inhibition is unclear. One of our prior studies suggests a global source: target proximity to the midpoint determines inhibition, consistent with the notion that oculomotor activation is responsible for the effect and the original definition of inhibition of return. A later study suggests a local source: target proximity to the nearest array element determines inhibition, consistent with the notion that repeat stimulation of an input pathway is responsible. To resolve the ambiguity we systematically test whether timing differences between studies altered the source of the inhibition. We find that both previously observed patterns are reproducible depending on the prime offset - target onset asynchrony. We also resolve the discrepancy by showing that when this asynchrony is less than 200 ms, target proximity to the array's midpoint and its proximity to any given array element can jointly determine inhibition, whereas when the asynchrony is approximately 200 ms, inhibition is robust at the midpoint of the array. At longer asynchronies, all inhibitory effects rapidly dissipate.
Christie, JohnHilchey, Matthew D.Klein, Raymond M.
11页
查看更多>>摘要：Oculomotor research shows that eye movements are primed toward the midpoint of an array of visual stimuli, such that an eye movement to a visual target is executed most rapidly when it appears near the midpoint of an earlier array. At longer intervals between the prime and target, this facilitatory effect can reverse to become inhibitory - such that eye movements are slower when made toward the midpoint - but the source of this inhibition is unclear. One of our prior studies suggests a global source: target proximity to the midpoint determines inhibition, consistent with the notion that oculomotor activation is responsible for the effect and the original definition of inhibition of return. A later study suggests a local source: target proximity to the nearest array element determines inhibition, consistent with the notion that repeat stimulation of an input pathway is responsible. To resolve the ambiguity we systematically test whether timing differences between studies altered the source of the inhibition. We find that both previously observed patterns are reproducible depending on the prime offset - target onset asynchrony. We also resolve the discrepancy by showing that when this asynchrony is less than 200 ms, target proximity to the array's midpoint and its proximity to any given array element can jointly determine inhibition, whereas when the asynchrony is approximately 200 ms, inhibition is robust at the midpoint of the array. At longer asynchronies, all inhibitory effects rapidly dissipate.
查看更多>>摘要：What is the effect of prior experience on sensorimotor behavior? We studied the following intriguing behavior: monkeys fixating a small target direct their gaze above the target if the background is dark. Fixating a target once on a bright background, then on a dark background, yields 2 gaze directions, typically one above the other; hence the name, 'dark-background-contingent upshift of gaze', which is abbreviated as 'upshift'. Is the upshift only an attempt to avoid using the fovea in the dark? If it is, we might expect to also observe a downshift and a sideshift. We studied gaze direction in a large group of 10 rhesus monkeys from Tubingen, to which we added published data from 4 cynomolgus monkeys from Rehovot. The upshift was ubiquitous, and there was no systematic sideshift. What is the function of the upshift? Is it related to vision in the dark? Here, we concentrate on the effect of the monkeys' previous training. Seven of the 14 monkeys were accustomed to working in the dark ('dark-habituated'), while the other 7 had worked in bright ambient light ('bright-habituated'). The main result of this study is that the dark-habituated monkeys had a much larger upshift: the mean upshift was 2.2 degrees in the dark-habituated monkeys, versus 0.5 degrees in the bright-habituated. Thus, the upshift depends on habituation; the size of the upshift reflects months-long cumulative experience. These findings suggest that the function of the upshift is indeed related to seeing in the dark.
查看更多>>摘要：What is the effect of prior experience on sensorimotor behavior? We studied the following intriguing behavior: monkeys fixating a small target direct their gaze above the target if the background is dark. Fixating a target once on a bright background, then on a dark background, yields 2 gaze directions, typically one above the other; hence the name, 'dark-background-contingent upshift of gaze', which is abbreviated as 'upshift'. Is the upshift only an attempt to avoid using the fovea in the dark? If it is, we might expect to also observe a downshift and a sideshift. We studied gaze direction in a large group of 10 rhesus monkeys from Tubingen, to which we added published data from 4 cynomolgus monkeys from Rehovot. The upshift was ubiquitous, and there was no systematic sideshift. What is the function of the upshift? Is it related to vision in the dark? Here, we concentrate on the effect of the monkeys' previous training. Seven of the 14 monkeys were accustomed to working in the dark ('dark-habituated'), while the other 7 had worked in bright ambient light ('bright-habituated'). The main result of this study is that the dark-habituated monkeys had a much larger upshift: the mean upshift was 2.2 degrees in the dark-habituated monkeys, versus 0.5 degrees in the bright-habituated. Thus, the upshift depends on habituation; the size of the upshift reflects months-long cumulative experience. These findings suggest that the function of the upshift is indeed related to seeing in the dark.
NSTL
Elsevier