scholarly journals Cortical magnification factor of human V2 predicts individual susceptibility to letter-crowding

2017 ◽  
Vol 17 (10) ◽  
pp. 396
Author(s):  
Steven Dakin ◽  
Samuel Schwarzkopf ◽  
Geraint Rees ◽  
Catherine Morgan ◽  
Elaine Anderson
Keyword(s):  
Magnification Factor ◽  
Individual Susceptibility ◽  
Cortical Magnification ◽  
Cortical Magnification Factor

scholarly journals SUVOKIAMO ATKARPOS ILGIO PRIKLAUSOMYBĖ NUO JOS ATVAIZDO VIETOS AKIES TINKLAINĖJE

Psichologija ◽  
2011 ◽  
Vol 43 ◽  
pp. 78-91
Author(s):  
A. Dzekevičiūtė ◽  
A. Daugirdienė ◽  
A. Švegžda ◽  
R. Stanikūnas ◽  
H. Vaitkevičius
Keyword(s):  
Visual Field ◽  
Line Length ◽  
The Other ◽  
Size Perception ◽  
Normal Vision ◽  
Magnification Factor ◽  
Extremum Point ◽  
Cortical Magnification ◽  
Cortical Magnification Factor ◽  
The Given

Tyrimo tikslas yra patikrinti, kaip keičiasi objekto dydžio suvokimas, kintant jo projekcijos padėčiai akies tinklainėje, ir kaip objekto dydžio suvokimas priklauso nuo akies tinklainės receptorių (kūgelių ir lazdelių) tankio. Tiriamieji, žiūrėdami viena akimi ir fiksuodami žvilgsnį, dalijo skirtingų ilgių atkarpas – nustatydavo suvokiamą vidurį. Atkarpos dalių santykio nuo atkarpos ilgio funkcija turėjo lūžio tašką (66,7 proc. tiriamiesiems, kai atkarpos ilgis 7 laipsniai, 23,33 proc. – 13 laipsnių, kiti neturėjo). Rezultatai aiškinami skirtingu kūgelių ir lazdelių tankiu akies tinklainėje ir skirtinga kūgelių ir lazdelių įtaka.Pagrindiniai žodžiai: dydžio suvokimas, žievinis didinimo veiksnys, fotoreceptorių tankis.Perceived Size of a Line Depending on Its Projection Place on the RetinaDzekevičiūtė A., Daugirdienė A., Švegžda A., Stanikūnas R., Vaitkevičius H. SummaryIt is known that objects located in the centre of the visual field are perceived as larger than the objects located in the periphery (Пиаже, 1978). The image of an object differs from its perception object. The perceived size of an object depends on the size of its image in the visual cortex. This stems from the so-called cortical magnification factor. It is assumed that the same quantity of receptors sends information to the same area of the cortex. But photoreceptors are different – rods and the cones. It is not clear whether the different type of receptors make a different influence on the above-mentioned distortion of mapping. Also, the image of the object on the retina is perceived differently, depending on its location on the retina. Our goal was to explore how this subjective expansion changes while moving away from the centre of the retina, because there are no data on this, phenomenon.Method. Thirty normal or corrected to normal vision adults participated in the study. Five different length lines (5, 7, 10, 13, 15 degrees) were represented on the computer’s monitor one line at a time. Participants had monoculary bisected lines into two subjectively equal parts fixating sight on a cross located at the given end of the line.Results. The ratio ρ (length of the line near the cross / length of the other part) was calculated. This ratio as a function of the length of the whole line was not monotonic: when the line was short, ρ decreased, but then it began to increase. Three groups of results were formed considering the ratio of the line length (where the function had the extremum point). The largest group (66.67%) had the extremum point when the line length was 7 deg. The second group (23.33%) had the extremum point when the line length was 13 deg. The last group (10%) had not clear extremum point and was excluded from the calculation. Changes of the ρ value cannot be explained by the perceptual instability of the length of the line (Brown, 1953). There could be a correlation between the value of ρ and the density of all receptors in the retina where the line was projected.Conclusions. Humans make a bias while monocular by bisecting a line: the part near the point of fixation is perceived as bigger than the other part. The function of the line size ratio changes not monotonically – it has an extremum point. Most often, the extremum point is observed when the line size is 7 deg. This point is near the point where the density of rods exceeds that of cones. Other subjects show the extremum point when line size is 13 deg., but the reasons for such a point shift remain unclear. Some subjects have no extremum point.Key words: size perception, cortical magnification factor, density of photoreceptors.

The Visual Stimulus for Saccadic Eye Movements in Human Observers

Perception ◽  
1980 ◽  
Vol 9 (1) ◽  
pp. 7-21 ◽  
Author(s):  
John M Findlay
Keyword(s):  
Temporal Change ◽  
Saccadic Eye Movements ◽  
Retinal Eccentricity ◽  
Magnification Factor ◽  
The Third ◽  
Spatial Frequencies ◽  
Average Luminance ◽  
Cortical Magnification ◽  
Equivalent Area ◽  
Cortical Magnification Factor

Three experiments are reported in which the salience of visual stimuli is assessed by finding which of two competing peripheral stimuli elicit a saccade when both are presented simultaneously with the use of a paradigm due to Lévy-Schoen. The first experiment shows how salience is affected by position in the visual field. A strong effect of retinal eccentricity is found which is compared with the cortical magnification factor. Additionally directional biases occur. The second experiment shows that temporal change appears to be significant in eliciting a saccade rather than any specific properties related to movement. The third experiment shows that contour at high spatial frequencies does not affect salience. An area of 4 cycles deg-1 high-contrast square-wave grating possesses the same salience as an equivalent area with identical, constant, space average luminance. Taken together, the results suggest that salience might be accountable for in terms of the activation of transient channels in the visual system.

Cortical magnification factor and the ganglion cell density of the primate retina

Nature ◽  
1989 ◽  
Vol 341 (6243) ◽  
pp. 643-646 ◽  
Author(s):  
Heinz Wässle ◽  
Ulrike Grünert ◽  
Jürgen Röhrenbeck ◽  
Brian B. Boycott
Keyword(s):  
Ganglion Cell ◽  
Cell Density ◽  
Magnification Factor ◽  
Cortical Magnification ◽  
Cortical Magnification Factor

scholarly journals Picturing Peripheral Acuity

Perception ◽  
1998 ◽  
Vol 27 (7) ◽  
pp. 817-825 ◽  
Author(s):  
Stuart Anstis
Keyword(s):  
Visual Field ◽  
Receptive Fields ◽  
Magnification Factor ◽  
Cortical Magnification ◽  
Retinal Receptive Fields ◽  
Cortical Magnification Factor

The grain of the retina becomes progressively coarser from the fovea to the periphery. This is caused by the decreasing number of retinal receptive fields and decreasing amount of cortex devoted to each degree of visual field (= cortical magnification factor) as one goes into the periphery. We simulate this with a picture that is progressively blurred towards its edges; when strictly fixated at its centre it looks equally sharp all over.

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