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Contour integration and aging: the effects of element spacing, orientation alignment and stimulus duration.

Roudaia E, Bennett PJ, Sekuler AB - Front Psychol (2013)

Bottom Line: Experiment 2 found that decreasing stimulus durations from 0.8 to 0.04 s had a greater effect on older subjects' performance, but only for less salient contours.As in Experiment, the effect of aging did not vary with absolute contour spacing.Decreasing the distracter spacing, however, had a greater detrimental effect on accuracy in older subjects compared to younger subjects.

View Article: PubMed Central - PubMed

Affiliation: Vision and Cognitive Neuroscience Lab, Department of Psychology, Neuroscience and Behaviour, McMaster University Hamilton, ON, Canada ; Institute of Neuroscience, Multisensory Cognition Research Group, Trinity College Dublin Dublin, Ireland.

ABSTRACT
The ability to extract contours in cluttered visual scenes, which is a crucial step in visual processing, declines with healthy aging, but the reasons for this decline are not well understood. In three experiments, we examined how the effect of aging on contour discrimination varies as a function of contour and distracter inter-element spacing, collinearity, and stimulus duration. Spiral-shaped contours composed of Gabors were embedded within a field of distracter Gabors of uniform density. In a four alternative forced-choice task, younger and older subjects were required to report the global orientation of the contour. In Experiment 1, the absolute contour element spacing varied from two to eight times the Gabor wavelength and contour element collinearity was disrupted with five levels of orientation jitter. Contour discrimination accuracy was lower in older subjects, but the effect of aging did not vary with contour spacing or orientation jitter. Experiment 2 found that decreasing stimulus durations from 0.8 to 0.04 s had a greater effect on older subjects' performance, but only for less salient contours. Experiment 3 examined the effect of the background on contour discrimination by varying the spacing and orientation of the distracter elements for contours with small and large absolute spacing. As in Experiment, the effect of aging did not vary with absolute contour spacing. Decreasing the distracter spacing, however, had a greater detrimental effect on accuracy in older subjects compared to younger subjects. Finally, both groups showed equally high accuracy when all distracters were iso-oriented. In sum, these findings suggest that aging does not affect the sensitivity of contour integration to proximity or collinearity. However, contour integration in older adults is slower and is especially vulnerable when distracters are denser than contour elements.

No MeSH data available.


Related in: MedlinePlus

Experiment 3 stimuli: spiral contours embedded in a background of randomly-oriented (A) or iso-oriented (B) Gabors with varying inter-element spacing. Contour elements had either 3λ (top row) or 6λ (bottom row) spacing. Distracter spacing varied from 1.5λ to 6.1λ, resulting in contour-distracter relative spacing ranging from 1.0 to 2.1. Three levels of relative spacing—1, 1.5, and 2.1—are shown here.
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Figure 6: Experiment 3 stimuli: spiral contours embedded in a background of randomly-oriented (A) or iso-oriented (B) Gabors with varying inter-element spacing. Contour elements had either 3λ (top row) or 6λ (bottom row) spacing. Distracter spacing varied from 1.5λ to 6.1λ, resulting in contour-distracter relative spacing ranging from 1.0 to 2.1. Three levels of relative spacing—1, 1.5, and 2.1—are shown here.

Mentions: Distracter elements were positioned randomly within the square stimulus area using an iterative procedure that maintained a pre-determined minimum separation between distracter elements. The iterative procedure continued until no more distracters could be placed. The 3λ contours were embedded in backgrounds with minimum distracter spacing of 2.9, 2.4, 2.0, 1.7, and 1.5λ. The 6λ contours were embedded in backgrounds with minimum distracter spacing of 6.1, 5.0, 4.0, 3.4, and 2.9λ. Thus, the relative spacing between contour and distracter elements were equal to 1.0, 1.2, 1.5, 1.8, or 2.1, where numbers greater than 1 indicate that contour spacing was larger than distracter spacing. The orientation of distracter elements varied in two conditions: random and iso-oriented. In the random condition, distacter orientations were sampled from a uniform distribution of angles from 0° to 360°. In the iso-oriented condition, each distracter orientation was sampled from a Gaussian normal distribution with σ = 5° and a mean that was equal to a randomly chosen angle between 0° and 360°. The iso-oriented background was tested only for relative spacing levels of 1.0 and 2.1, and the randomly-oriented background was tested with all five levels of relative spacing. Examples of stimuli are shown in Figure 6.


Contour integration and aging: the effects of element spacing, orientation alignment and stimulus duration.

Roudaia E, Bennett PJ, Sekuler AB - Front Psychol (2013)

Experiment 3 stimuli: spiral contours embedded in a background of randomly-oriented (A) or iso-oriented (B) Gabors with varying inter-element spacing. Contour elements had either 3λ (top row) or 6λ (bottom row) spacing. Distracter spacing varied from 1.5λ to 6.1λ, resulting in contour-distracter relative spacing ranging from 1.0 to 2.1. Three levels of relative spacing—1, 1.5, and 2.1—are shown here.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3687141&req=5

Figure 6: Experiment 3 stimuli: spiral contours embedded in a background of randomly-oriented (A) or iso-oriented (B) Gabors with varying inter-element spacing. Contour elements had either 3λ (top row) or 6λ (bottom row) spacing. Distracter spacing varied from 1.5λ to 6.1λ, resulting in contour-distracter relative spacing ranging from 1.0 to 2.1. Three levels of relative spacing—1, 1.5, and 2.1—are shown here.
Mentions: Distracter elements were positioned randomly within the square stimulus area using an iterative procedure that maintained a pre-determined minimum separation between distracter elements. The iterative procedure continued until no more distracters could be placed. The 3λ contours were embedded in backgrounds with minimum distracter spacing of 2.9, 2.4, 2.0, 1.7, and 1.5λ. The 6λ contours were embedded in backgrounds with minimum distracter spacing of 6.1, 5.0, 4.0, 3.4, and 2.9λ. Thus, the relative spacing between contour and distracter elements were equal to 1.0, 1.2, 1.5, 1.8, or 2.1, where numbers greater than 1 indicate that contour spacing was larger than distracter spacing. The orientation of distracter elements varied in two conditions: random and iso-oriented. In the random condition, distacter orientations were sampled from a uniform distribution of angles from 0° to 360°. In the iso-oriented condition, each distracter orientation was sampled from a Gaussian normal distribution with σ = 5° and a mean that was equal to a randomly chosen angle between 0° and 360°. The iso-oriented background was tested only for relative spacing levels of 1.0 and 2.1, and the randomly-oriented background was tested with all five levels of relative spacing. Examples of stimuli are shown in Figure 6.

Bottom Line: Experiment 2 found that decreasing stimulus durations from 0.8 to 0.04 s had a greater effect on older subjects' performance, but only for less salient contours.As in Experiment, the effect of aging did not vary with absolute contour spacing.Decreasing the distracter spacing, however, had a greater detrimental effect on accuracy in older subjects compared to younger subjects.

View Article: PubMed Central - PubMed

Affiliation: Vision and Cognitive Neuroscience Lab, Department of Psychology, Neuroscience and Behaviour, McMaster University Hamilton, ON, Canada ; Institute of Neuroscience, Multisensory Cognition Research Group, Trinity College Dublin Dublin, Ireland.

ABSTRACT
The ability to extract contours in cluttered visual scenes, which is a crucial step in visual processing, declines with healthy aging, but the reasons for this decline are not well understood. In three experiments, we examined how the effect of aging on contour discrimination varies as a function of contour and distracter inter-element spacing, collinearity, and stimulus duration. Spiral-shaped contours composed of Gabors were embedded within a field of distracter Gabors of uniform density. In a four alternative forced-choice task, younger and older subjects were required to report the global orientation of the contour. In Experiment 1, the absolute contour element spacing varied from two to eight times the Gabor wavelength and contour element collinearity was disrupted with five levels of orientation jitter. Contour discrimination accuracy was lower in older subjects, but the effect of aging did not vary with contour spacing or orientation jitter. Experiment 2 found that decreasing stimulus durations from 0.8 to 0.04 s had a greater effect on older subjects' performance, but only for less salient contours. Experiment 3 examined the effect of the background on contour discrimination by varying the spacing and orientation of the distracter elements for contours with small and large absolute spacing. As in Experiment, the effect of aging did not vary with absolute contour spacing. Decreasing the distracter spacing, however, had a greater detrimental effect on accuracy in older subjects compared to younger subjects. Finally, both groups showed equally high accuracy when all distracters were iso-oriented. In sum, these findings suggest that aging does not affect the sensitivity of contour integration to proximity or collinearity. However, contour integration in older adults is slower and is especially vulnerable when distracters are denser than contour elements.

No MeSH data available.


Related in: MedlinePlus