Visual motion processing in one-month-old infants: Preferential looking experiments

AbstractThe ability of infants to discriminate between opposite directions of motion was assessed using forced-choice preferential looking between a random-dot pattern which was segregated into regions which moved in opposite directions, and a uniform pattern in which all the dots moved in the same direction. The first experiment measured velocity thresholds ( νmin and νmax) for direction discrimination; between 10 and 13 weeks νmin decreased, while at the same time νmax increased. The second experiment explored possible implications of this expanding velocity range for direction discrimination by younger infants. One-month-olds showed no evidence for direction discrimination at any of a number of test velocities in the range 1–43 deg/sec. The 1-month-olds were also tested with two additional conditions: they could discriminate between moving and static patterns at velocities of 10 deg/sec or above, and they could also discriminate between coherent and incoherent motion at velocities of 21 deg/sec or below. Neither of these discriminations depends on sensitivity to the direction of the coherent motion. The results suggest that 1-month-olds may not be sensitive to the direction of visual motion

The Development of Visual Motion Processing in Human Infants

The experiments of this thesis have used apparent motion in random-dot patterns to explore the development of motion processing in infants. Most of the experiments involved discrimination of a segregated pattern, in which different regions moved in different ways (eg opposite directions), from a uniform pattern containing just one kind of motion. Maximum displacement limits (dmax) for discrimination of coherent from incoherent motion, and for discrimination of opposite directions of coherent motion, increased between 8 and 15 weeks. The higher threshold of adults indicated that this increase continues beyond 15 weeks. The effect of changing the interval between displacements indicated two processes underlying the increase in direction discrimination dmax: a maturation of the temporal properties of motion detectors (eg improving sensitivity to high temporal frequencies), which is largely complete by about 12 weeks; and a more prolonged development of their spatial properties which dominates the change in dmax after 12 weeks, and may also be involved before this. Measurements of coherence thresholds for direction discrimination showed that, in addition to the rise in dmax with age, there is a substantial improvement in motion sensitivity at displacements below dmax. Hence a uniform increase in sensitivity across all displacements is likely to be an important factor behind the development of dmax. However there may be additional specific improvements in sensitivity to large displacements, perhaps reflecting the emergence of low spatial frequency channels. A series of habituation and preferential looking experiments failed to find evidence for direction discrimination before 6 weeks, though positive evidence was obtained at 6-8 weeks. The results suggest that directionality emerges at about 7 weeks of age. Interestingly, despite their success at discriminating direction in a segregated stimulus, 6-8-week-olds were insensitive to the absolute direction of uniform motion. This suggests that they have not yet learnt to combine measurements of retinal image motion with information about eye movements

Differential human brain activation by vertical and horizontal global visual textures

Mid-level visual processes which integrate local orientation information for the detection of global structure can be investigated using global form stimuli of varying complexity. Several lines of evidence suggest that the identification of concentric and parallel organisations relies on different underlying neural substrates. The current study measured brain activation by concentric, horizontal parallel, and vertical parallel arrays of short line segments, compared to arrays of randomly oriented segments. Six subjects were scanned in a blocked design functional magnetic resonance imaging experiment. We compared percentage BOLD signal change during the concentric, horizontal and vertical blocks within early retinotopic areas, the fusiform face area and the lateral occipital complex. Unexpectedly, we found that vertical and horizontal parallel forms differentially activated visual cortical areas beyond V1, but in general, activations to concentric and parallel forms did not differ. Vertical patterns produced the highest percentage signal change overall and only area V3A showed a significant difference between concentric and parallel (horizontal) stimuli, with the former better activating this area. These data suggest that the difference in brain activation to vertical and horizontal forms arises at intermediate or global levels of visual representation since the differential activity was found in mid-level retinotopic areas V2 and V3 but not in V1. This may explain why earlier studies—using methods that emphasised responses to local orientation—did not discover this vertical-horizontal anisotrop

Cortical Processing of Global Form, Motion and Biological Motion Under Low Light Levels

Advances in potential treatments for rod and cone dystrophies have increased the need to understand the contributions of rods and cones to higher-level cortical vision. We measured form, motion and biological motion coherence thresholds and EEG steady-state visual evoked potentials (SSVEP) responses under light conditions ranging from photopic to scotopic. Low light increased thresholds for all three kinds of stimuli; however, global form thresholds were relatively more impaired than those for global motion or biological motion. SSVEP responses to coherent global form and motion were reduced in low light, and motion responses showed a shift in topography from the midline to more lateral locations. Contrast sensitivity measures confirmed that basic visual processing was also affected by low light. However, comparison with contrast sensitivity function (CSF) reductions achieved by optical blur indicated that these were insufficient to explain the pattern of results, although the temporal properties of the rod system may also play a role. Overall, mid-level processing in extra-striate areas is differentially affected by light level, in ways that cannot be explained in terms of low-level spatiotemporal sensitivity. A topographical shift in scotopic motion SSVEP responses may reflect either changes to inhibitory feedback mechanisms between V1 and extra-striate regions or a reduction of input to the visual cortex. These results provide insight into how higher-level cortical vision is normally organised in absence of cone input, and provide a basis for comparison with patients with cone dystrophies, before and after treatments aiming to restore cone function

Differential human brain activation by vertical and horizontal global visual textures

Mid-level visual processes which integrate local orientation information for the detection of global structure can be investigated using global form stimuli of varying complexity. Several lines of evidence suggest that the identification of concentric and parallel organisations relies on different underlying neural substrates. The current study measured brain activation by concentric, horizontal parallel, and vertical parallel arrays of short line segments, compared to arrays of randomly oriented segments. Six subjects were scanned in a blocked design functional magnetic resonance imaging experiment. We compared percentage BOLD signal change during the concentric, horizontal and vertical blocks within early retinotopic areas, the fusiform face area and the lateral occipital complex. Unexpectedly, we found that vertical and horizontal parallel forms differentially activated visual cortical areas beyond V1, but in general, activations to concentric and parallel forms did not differ. Vertical patterns produced the highest percentage signal change overall and only area V3A showed a significant difference between concentric and parallel (horizontal) stimuli, with the former better activating this area. These data suggest that the difference in brain activation to vertical and horizontal forms arises at intermediate or global levels of visual representation since the differential activity was found in mid-level retinotopic areas V2 and V3 but not in V1. This may explain why earlier studies--using methods that emphasised responses to local orientation--did not discover this vertical-horizontal anisotropy

Sensitive Period for a Multimodal Response in Human Visual Motion Area

The middle temporal complex (MT/MST) is a brain region specialized for the perception of motion in the visual modality [ [1], [2], [3] and [4]]. However, this specialization is modified by visual experience: after long-standing blindness, MT/MST responds to sound [5]. Recent evidence also suggests that the auditory response of MT/MST is selective for motion [ [6] and [7]]. The developmental time course of this plasticity is not known. To test for a sensitive period in MT/MST development, we used fMRI to compare MT/MST function in congenitally blind, late-blind, and sighted adults. MT/MST responded to sound in congenitally blind adults, but not in late-blind or sighted adults, and not in an individual who lost his vision between ages of 2 and 3 years. All blind adults had reduced functional connectivity between MT/MST and other visual regions. Functional connectivity was increased between MT/MST and lateral prefrontal areas in congenitally blind relative to sighted and late-blind adults. These data suggest that early blindness affects the function of feedback projections from prefrontal cortex to MT/MST. We conclude that there is a sensitive period for visual specialization in MT/MST. During typical development, early visual experience either maintains or creates a vision-dominated response. Once established, this response profile is not altered by long-standing blindness.David and Lucille Packard FoundationNational Center for Research Resources: Harvard-Thorndike General Clinical Research Center at Beth Israel Deaconess Medical Center (NCRR MO1 RR01032)Harvard Clinical and Translational Science Center (UL1 RR025758)National Institutes of Health (U.S.) (grant K24 RR018875)National Institutes of Health (U.S.) (grant RO1-EY12091

Development of radial optic flow pattern sensitivity at different speeds

AbstractThe development of sensitivity to radial optic flow discrimination was investigated by measuring motion coherence thresholds (MCTs) in school-aged children at two speeds. A total of 119 child observers aged 6–16years and 24 young adult observers (23.66+/−2.74years) participated. In a 2AFC task observers identified the direction of motion of a 5° radial (expanding vs. contracting) optic flow pattern containing 100 dots with 75% Michelson contrast moving at 1.6°/s and 5.5°/s and. The direction of each dot was drawn from a Gaussian distribution whose standard deviation was either low (similar directions) or high (different directions). Adult observers also identified the direction of motion for translational (rightward vs. leftward) and rotational (clockwise vs. anticlockwise) patterns. Motion coherence thresholds to radial optic flow improved gradually with age (linear regression, p<0.05), with different rates of development at the two speeds. Even at 16years MCTs were higher than that for adults (independent t-tests, p<0.05). Both children and adults had higher sensitivity at 5.5°/s compared to 1.6°/s (paired t-tests, p<0.05). Sensitivity to radial optic flow is still immature at 16years of age, indicating late maturation of higher cortical areas. Differences in sensitivity and rate of development of radial optic flow at the different speeds, suggest that different motion processing mechanisms are involved in processing slow and fast speeds

The development of contour processing : evidence from physiology and psychophysics

Object perception and pattern vision depend fundamentally upon the extraction of contours from the visual environment. In adulthood, contour or edge-level processing is supported by the Gestalt heuristics of proximity, collinearity, and closure. Less is known, however, about the developmental trajectory of contour detection and contour integration. Within the physiology of the visual system, long-range horizontal connections in V1 and V2 are the likely candidates for implementing these heuristics. While post-mortem anatomical studies of human infants suggest that horizontal interconnections reach maturity by the second year of life, psychophysical research with infants and children suggests a considerably more protracted development. In the present review, data from infancy to adulthood will be discussed in order to track the development of contour detection and integration. The goal of this review is thus to integrate the development of contour detection and integration with research regarding the development of underlying neural circuitry.We conclude that the ontogeny of this system is best characterized as a developmentally extended period of associative acquisition whereby horizontal connectivity becomes functional over longer and longer distances, thus becoming able to effectively integrate over greater spans of visual space. Keywords

The development and learning of the visual control of movement: An ecological perspective

We compare development and learning of the visual control of movement from an ecological perspective. It is argued that although the constraints that are imposed upon development and learning are vastly different, both are best characterised as a change towards the use of more useful and specifying optic variables. Implicit learning, in which awareness is drawn away from movement execution, is most appropriate to accomplish this change in optic variable use, although its contribution in development is more contentious. Alternatively, learning can also be affected by explicit processes. We propose that explicit learning would typically invoke vision for perception processes instead of the designated vision for action processes. It is for that reason that after explicit learning performance is more easily compromised in the face of pressure or disorders. We present a way to deal with the issue of explicit learning during infancy. © 2003 Elsevier Inc. All rights reserved