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Radial frequency stimuli and sine-wave gratings seem to be processed by distinct contrast brain mechanisms.
| Content Provider | Semantic Scholar |
|---|---|
| Author | Simas, Moana Nogueira, Renata Maria Toscano Barreto Lyra Santos, N. A. |
| Copyright Year | 2005 |
| Abstract | An assumption commonly made in the study of visual perception is that the lower the contrast threshold for a given stimulus, the more sensitive and selective will be the mechanism that processes it. On the basis of this consideration, we investigated contrast thresholds for two classes of stimuli: sine-wave gratings and radial frequency stimuli (i.e., j0 targets or stimuli modulated by spherical Bessel functions). Employing a suprathreshold summation method, we measured the selectivity of spatial and radial frequency filters using either sine-wave gratings or j0 target contrast profiles at either 1 or 4 cycles per degree of visual angle (cpd), as the test frequencies. Thus, in a forced-choice trial, observers chose between a background spatial (or radial) frequency alone and the given background stimulus plus the test frequency (1 or 4 cpd sine-wave grating or radial frequency). Contrary to our expectations, the results showed elevated thresholds (i.e., inhibition) for sine-wave gratings and decreased thresholds (i.e., summation) for radial frequencies when background and test frequencies were identical. This was true for both 1- and 4-cpd test frequencies. This finding suggests that sine-wave gratings and radial frequency stimuli are processed by different quasi-linear systems, one working at low luminance and contrast level (sine-wave gratings) and the other at high luminance and contrast levels (radial frequency stimuli). We think that this interpretation is consistent with distinct foveal only and foveal-parafoveal mechanisms involving striate and/or other higher visual areas (i.e., V2 and V4). |
| Starting Page | 585 |
| Ending Page | 600 |
| Page Count | 16 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://scielo.br/pdf/bjmbr/v38n3/5387.pdf?origin=publication_detail |
| Alternate Webpage(s) | http://www.scielo.br/pdf/bjmbr/v38n3/5387.pdf |
| PubMed reference number | 15761622v1 |
| Volume Number | 38 |
| Issue Number | 3 |
| Journal | Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Class Short Interspersed Nucleotide Elements Summation (document) Summation (function) Vision |
| Content Type | Text |
| Resource Type | Article |
