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The ups and downs of global motion perception: a paradoxical advantage for smaller stimuli in the aging visual system.

Hutchinson CV, Ledgeway T, Allen HA - Front Aging Neurosci (2014)

Bottom Line: We found that older adults' performance was relatively unaffected by changes in aperture size, the number and density of local elements in the display.These findings suggest that the normal (disease-free) aging process does not lead to a general decline in perceptual ability and in some cases may be visually advantageous.These include age-related changes in spatial summation, reduced cortical inhibition, neural blur and attentional resource allocation.

View Article: PubMed Central - PubMed

Affiliation: College of Medicine, Biological Sciences and Psychology, School of Psychology, University of Leicester Leicester, UK.

ABSTRACT
Recent evidence suggests that normal aging is typically accompanied by impairment in the ability to perceive the global (overall) motion of visual objects in the world. The purpose of this study was to examine the interplay between age-related changes in the ability to perceive translational global motion (up vs. down) and important factors such as the spatial extent (size) over which movement occurs and how cluttered the moving elements are (density). We used random dot kinematograms (RDKs) and measured motion coherence thresholds (% signal elements required to reliably discriminate global direction) for young and older adults. We did so as a function of the number and density of local signal elements, and the aperture area in which they were displayed. We found that older adults' performance was relatively unaffected by changes in aperture size, the number and density of local elements in the display. In young adults, performance was also insensitive to element number and density but was modulated markedly by display size, such that motion coherence thresholds decreased as aperture area increased (participants required fewer local elements to move coherently to determine the overall image direction). With the smallest apertures tested, young participants' motion coherence thresholds were considerably higher (~1.5 times worse) than those of their older counterparts. Therefore, when RDK size is relatively small, older participants were actually better than young participants at processing global motion. These findings suggest that the normal (disease-free) aging process does not lead to a general decline in perceptual ability and in some cases may be visually advantageous. The results have important implications for the understanding of the consequences of aging on visual function and a number of potential explanations are explored. These include age-related changes in spatial summation, reduced cortical inhibition, neural blur and attentional resource allocation.

No MeSH data available.


Related in: MedlinePlus

Examples of stimulus composition. (A) Experiment 1: Dot number remained constant irrespective of aperture size such that dot density decreased as aperture size increased. (B) Experiment 2: Dot number increased with increasing aperture size such that dot density remained constant. (C) Experiment 3: Dot number varied and aperture size remained constant such that increasing dot number led to an increase in dot density.
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Figure 1: Examples of stimulus composition. (A) Experiment 1: Dot number remained constant irrespective of aperture size such that dot density decreased as aperture size increased. (B) Experiment 2: Dot number increased with increasing aperture size such that dot density remained constant. (C) Experiment 3: Dot number varied and aperture size remained constant such that increasing dot number led to an increase in dot density.

Mentions: Stimuli were generated using a Macintosh G4 and presented on a P255f Professional monitor (refresh rate 75 Hz) that was gamma-corrected with the aid of internal look-up tables. Stimuli were RDKs depicting translational (up vs. down) motion. Dots (0.47 deg diameter) were high contrast (30% Michelson) and were presented in a central aperture on a homogenous “gray” background (background luminance 64.72 cd/m2). Viewing distance was 92 cm. Each RDK was generated immediately prior to its presentation and was composed of a sequence of 8 images (each 53.3 ms), which when presented consecutively produced continuous motion lasting 426.7 ms. At the beginning of each motion sequence, the position of each dot was randomly assigned. On subsequent frames, each dot was shifted by 0.3 deg, resulting in a drift speed of 5.7 deg/s. When a dot dropped off the edge of the circular display window it was immediately re-plotted in a random spatial position within the window. In Experiment 1, aperture area varied in the range 28–227 deg2 but dot number remained constant (64 dots), such that a two-fold increase in aperture area corresponded to a two-fold decrease in dot density (in the range 2.26–0.28 dots/deg2). In Experiment 2, aperture area varied from 14 to 227 deg2 but dot density remained constant (1.13 dots/deg2) across experimental conditions, such that a two-fold increase in aperture area corresponded to an equivalent increase in dot number (in the range 16–256 dots). In Experiment 3, aperture area remained constant at 113 deg2 and two dot densities (0.44 and 1.13 dots/deg2) were presented. A stimulus schematic for each experiment is shown in Figure 1.


The ups and downs of global motion perception: a paradoxical advantage for smaller stimuli in the aging visual system.

Hutchinson CV, Ledgeway T, Allen HA - Front Aging Neurosci (2014)

Examples of stimulus composition. (A) Experiment 1: Dot number remained constant irrespective of aperture size such that dot density decreased as aperture size increased. (B) Experiment 2: Dot number increased with increasing aperture size such that dot density remained constant. (C) Experiment 3: Dot number varied and aperture size remained constant such that increasing dot number led to an increase in dot density.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126366&req=5

Figure 1: Examples of stimulus composition. (A) Experiment 1: Dot number remained constant irrespective of aperture size such that dot density decreased as aperture size increased. (B) Experiment 2: Dot number increased with increasing aperture size such that dot density remained constant. (C) Experiment 3: Dot number varied and aperture size remained constant such that increasing dot number led to an increase in dot density.
Mentions: Stimuli were generated using a Macintosh G4 and presented on a P255f Professional monitor (refresh rate 75 Hz) that was gamma-corrected with the aid of internal look-up tables. Stimuli were RDKs depicting translational (up vs. down) motion. Dots (0.47 deg diameter) were high contrast (30% Michelson) and were presented in a central aperture on a homogenous “gray” background (background luminance 64.72 cd/m2). Viewing distance was 92 cm. Each RDK was generated immediately prior to its presentation and was composed of a sequence of 8 images (each 53.3 ms), which when presented consecutively produced continuous motion lasting 426.7 ms. At the beginning of each motion sequence, the position of each dot was randomly assigned. On subsequent frames, each dot was shifted by 0.3 deg, resulting in a drift speed of 5.7 deg/s. When a dot dropped off the edge of the circular display window it was immediately re-plotted in a random spatial position within the window. In Experiment 1, aperture area varied in the range 28–227 deg2 but dot number remained constant (64 dots), such that a two-fold increase in aperture area corresponded to a two-fold decrease in dot density (in the range 2.26–0.28 dots/deg2). In Experiment 2, aperture area varied from 14 to 227 deg2 but dot density remained constant (1.13 dots/deg2) across experimental conditions, such that a two-fold increase in aperture area corresponded to an equivalent increase in dot number (in the range 16–256 dots). In Experiment 3, aperture area remained constant at 113 deg2 and two dot densities (0.44 and 1.13 dots/deg2) were presented. A stimulus schematic for each experiment is shown in Figure 1.

Bottom Line: We found that older adults' performance was relatively unaffected by changes in aperture size, the number and density of local elements in the display.These findings suggest that the normal (disease-free) aging process does not lead to a general decline in perceptual ability and in some cases may be visually advantageous.These include age-related changes in spatial summation, reduced cortical inhibition, neural blur and attentional resource allocation.

View Article: PubMed Central - PubMed

Affiliation: College of Medicine, Biological Sciences and Psychology, School of Psychology, University of Leicester Leicester, UK.

ABSTRACT
Recent evidence suggests that normal aging is typically accompanied by impairment in the ability to perceive the global (overall) motion of visual objects in the world. The purpose of this study was to examine the interplay between age-related changes in the ability to perceive translational global motion (up vs. down) and important factors such as the spatial extent (size) over which movement occurs and how cluttered the moving elements are (density). We used random dot kinematograms (RDKs) and measured motion coherence thresholds (% signal elements required to reliably discriminate global direction) for young and older adults. We did so as a function of the number and density of local signal elements, and the aperture area in which they were displayed. We found that older adults' performance was relatively unaffected by changes in aperture size, the number and density of local elements in the display. In young adults, performance was also insensitive to element number and density but was modulated markedly by display size, such that motion coherence thresholds decreased as aperture area increased (participants required fewer local elements to move coherently to determine the overall image direction). With the smallest apertures tested, young participants' motion coherence thresholds were considerably higher (~1.5 times worse) than those of their older counterparts. Therefore, when RDK size is relatively small, older participants were actually better than young participants at processing global motion. These findings suggest that the normal (disease-free) aging process does not lead to a general decline in perceptual ability and in some cases may be visually advantageous. The results have important implications for the understanding of the consequences of aging on visual function and a number of potential explanations are explored. These include age-related changes in spatial summation, reduced cortical inhibition, neural blur and attentional resource allocation.

No MeSH data available.


Related in: MedlinePlus