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Results for “Size Perception”

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At least 73 records · Page 4Linked to original sources
PubMed1994

Food photography. I: The perception of food portion size from photographs.

Fifty-one male and female volunteers aged 18-90 years from a wide variety of social and occupational backgrounds completed 7284 assessments of portion size in relation to food photographs. Subjects were shown six portion sizes (two small, two medium and two large) for each of six foods, and asked to compare the amount on the plate in front of them to (a) a series of eight photographs showing weights of portions from the 5th to the 95th centile of portion size (British Adult Dietary Survey), or (b) a single photograph of the average (median) portion size. Photographs were prepared either in colour or in black and white, and in two different sizes. The order of presentation of foods; use of black and white or colour; the size of photographs; and presentation of eight or average photographs were each randomized independently. On average, the mean differences between the portion size presented and the estimate of portion size using the photographs varied from -8 to +6 g (-4 to +5%) for the series of eight photographs, and from -34 to -1 g (-23 to +9%) for the single average photograph. Large portion sizes tended to be underestimated more than medium or small portion sizes, especially when using the average photograph (from -79 to -14 g, -37 to -13%). Being female, 65 years and over, or retired, or seeing photographs in colour, were all associated with small but statistically significant overestimations of portion size. Having a body mass index > or = 30 kg/m2 was associated with an 8% underestimate of portion size. We conclude that use of a series of eight photographs is associated with relatively small errors in portion size perception, whereas use of an average photograph is consistently associated with substantial underestimation across a variety of foods.

Adolescent↗
PubMed1979

Perception of size of one object among many.

Adaptation to a grating of properly chosen frequency may lead to two apparently conflicting observations: Another grating may then appear to be of increased frequency (compared with its "unadapted" frequency) while the individual bars of the grating appear to have widened. This perceived widening parallels previous results with single bars. By attending to only one grating bar, the subject effectively seems to change the grating frequency spectrum to that of a single bar.

Adaptation, Physiological↗
PubMedDate not supplied

Prehension and perception of size in left visual neglect.

Right hemisphere damaged patients with and without left visual neglect, and age-matched controls had objects of various sizes presented within left or right body hemispace. Subjects were asked to estimate the objects' sizes or to reach out and grasp them, in order to assess visual size processing in perceptual-experiential and action-based contexts respectively. No impairments of size processing were detected in the prehension performance of the neglect patients but a generalised slowing of movement was observed, associated with an extended deceleration phase. Additionally both patient groups reached maximum grip aperture relatively later in the movement than did controls. For the estimation task it was predicted that the left visual neglect group would systematically underestimate the sizes of objects presented within left hemispace but no such abnormalities were observed. Possible reasons for this unexpected null finding are discussed.

Aged↗
PubMed2001

Cuttlefish camouflage: visual perception of size, contrast and number of white squares on artificial checkerboard substrata initiates disruptive coloration.

We investigated some visual background features that influence young cuttlefish, Sepia pharaonis, to change their skin patterning from 'general resemblance' of the substratum to disruptive coloration that breaks up their body form. Using computer-generated black/white checkerboard patterns as substrata, we first found that the size of the white squares had to be within a certain narrow range (relative to the size of the cuttlefish 'white square') for the animal to exhibit disruptive skin patterning. Second, given the appropriate size of checker, cuttlefish regulated their disruptive skin patterns according to the contrast between white and black squares. Third, by manipulating the number of white squares on a black background, we found that as few as four white squares among 316 black squares (or 1.25%) produced disruptive patterning, yet increasing the number of white squares to 20, 40 or 80 did not increase the frequency of appearance of the cuttlefish 'white square', but only its clarity of expression. These results demonstrate that the size, contrast and number of white objects in the surrounding substratum influence the production and expression of disruptive skin patterns in young cuttlefish.

Animals↗
PubMed2003

Hemispace differences in the visual perception of size in left hemiParkinson's disease.

The visual perception of size in different regions of external space was studied in Parkinson's disease (PD). A group of patients with worse left-sided symptoms (LPD) was compared with a group with worse right-sided symptoms (RPD) and with a group of age-matched controls on judgements of the relative height or width of two rectangles presented in different regions of external space. The relevant dimension of one rectangle (the 'standard') was held constant, while that of the other (the 'variable') was varied in a method of constant stimuli. The point of subjective equality (PSE) of rectangle width or height was obtained by probit analysis as the mean of the resulting psychometric function. When the standard was in left space, the PSE of the LPD group occurred when the variable was smaller, and when the standard was in right space, when the variable was larger. Similarly, when the standard rectangle was presented in upper space, and the variable in lower space, the PSE occurred when the variable was smaller, an effect which was similar in both left and right spaces. In all these experiments, the PSEs for both the controls and the RPD group did not differ significantly, and were close to a physical match, and the slopes of the psychometric functions were steeper in the controls than the patients, though not significantly so. The data suggest that objects appear smaller in the left and upper visual spaces in LPD, probably because of right hemisphere impairment.

Aged↗
PubMed2005

Chromatic perceptive field sizes change with retinal illuminance.

The effect of retinal illuminance (0.3-3.3 log td) on chromatic perceptive field size was investigated at 10 degrees eccentricity along the horizontal meridian of the temporal retina. Using the 4+1 color-naming procedure, observers described the hue and saturation of a series of monochromatic stimuli (440-660 nm, in 10-nm steps) of various test sizes (.098-5 degrees) after 30-min dark adaptation. Perceptive field sizes of the four elemental hues and the saturation component were estimated for each wavelength at each retinal illuminance. Results indicate that perceptive field sizes for blue, green, yellow, and saturation all decrease with increasing retinal illuminance; the perceptive field size for red is the smallest and invariant with intensity. The influence of rods on perceptive field size may account for some of the results; other factors are also considered.

Adult↗
PubMed1977

Pictorial perspective: perception of size, linear, and texture perspective in children and adults.

Perception of size, linear, and texture perspective was investigated in third-grade and sixth-grade children and in college adults in three separate studies. A matching task required the observer to choose from a set of four alternative real scenes the correct match for the test stimulus, which was either a picture or a real scene. Correct performance required that the subject utilize perspective information for both size and distance distance relations. Erroneous choices available to the subject indicated errors in size judgement, in distance judgment, or in both simultaneously. View was either restricted at the correct station point or was free, with head motion. There were no significant effects of grade level. For all three groups, mean percent correct was nearly 100% with the real-scene test stimuli, and significantly below the chance level with the picture test stimuli. Errors in size judgment occurred most frequently, indicating that the geometrically correct rate of perspective convergence was too rapid to be seen by the subjects as perceptually acceptable. With size-perspective information alone, the number of size plus distance errors also increased significantly. There was no significant effect of viewing condition.

Adult↗
PubMed2005

Effect of stimulus intensity on the sizes of chromatic perceptive fields.

The effects of intensity on chromatic perceptive field size were investigated along the horizontal meridian at 10 degrees temporal eccentricity by manipulating stimulus intensity from 0.3 to 3.3 log trolands. Following light adaptation, observers described the hue and saturation of monochromatic stimuli (440-660 nm, in 10 nm steps) for a series of test sizes (0.098-3 degrees) presented along the time period associated with the cone plateau of the dark-adaptation function. Perceptive field sizes of the four elemental hues (red, green, yellow, and blue) and the saturation component were estimated by three observers at each intensity level for each wavelength. In general, perceptive field sizes of blue and red are the smallest, and yellow and green are the largest. Furthermore, perceptive field sizes of all four hues decrease with increasing stimulus intensity, though the absolute change is largest for green and yellow. The decrease in size with increase in intensity cannot be completely explained in terms of saturation or rod signals and is likely, then, attributable to a cone-based mechanism.

Adaptation, Ocular↗
PubMed1979

Shifts in perception of size after adaptation to gratings.

After viewing a suitable grating of vertical stripes for 5 minutes, subjects overestimated the width of a rectangle by 6 percent. The shifts in perception of size occurred whether individual stripes in the grating were narrower than, equal to, or wider than the rectangle. Rectangle width was underestimated only if the grating stripes were extremely wide, with a spatial frequency lower than most of the effective amplitude spectrum of the rectangle. These findings (and complementary ones with horizontal gratings) suggest that the visual system codes size on the basis of spatial frequency components, rather than directly in terms of width.

Adaptation, Physiological↗
PubMed2003

Biological motion as a cue for the perception of size.

Animals as well as humans adjust their gait patterns in order to minimize energy required for their locomotion. A particularly important factor is the constant force of earth's gravity. In many dynamic systems, gravity defines a relation between temporal and spatial parameters. The stride frequency of an animal that moves efficiently in terms of energy consumption depends on its size. In two psychophysical experiments, we investigated whether human observers can employ this relation in order to retrieve size information from point-light displays of dogs moving with varying stride frequencies across the screen. In Experiment 1, observers had to adjust the apparent size of a walking point-light dog by placing it at different depths in a three-dimensional depiction of a complex landscape. In Experiment 2, the size of the dog could be adjusted directly. Results show that displays with high stride frequencies are perceived to be smaller than displays with low stride frequencies and that this correlation perfectly reflects the predicted inverse quadratic relation between stride frequency and size. We conclude that biological motion can serve as a cue to retrieve the size of an animal and, therefore, to scale the visual environment.

Adult↗