Biomedical subjects

Alex K Nugent

Publications and source records attributed to Alex K Nugent.

2 recordsLinked to original sources

PubMed2003

Contour integration in peripheral vision reduces gradually with eccentricity.

Hess and Dakin reported that normally-sighted subjects using peripheral vision (beyond 10 degrees ) were unable to detect paths of alternating-phase Gabors embedded within randomly positioned Gabors, but could detect same-phase paths. This result led them to propose a "fundamental difference" between central and peripheral visual processing. While we were able to replicate many of their results, our normally-sighted observers could detect alternating-phase paths beyond 10 degrees. We found that path detection decreased monotonically as a function of eccentricity (0 degrees -30 degrees ) for both alternating-phase and same-phase stimuli. As with most visual functions the more difficult path detection condition (alternating-phase) declined slightly faster. The results for the normally-sighted observers could not be explained by poor fixation. Three people with substantial central vision loss (i.e. they can only use peripheral vision) could see both same- and alternating-phase stimuli with eccentric viewing of 13 degrees -17 degrees. Therefore central and peripheral vision appear to use similar visual mechanisms to perform the task, there being no fundamental difference.

Adult↗

PubMed2002

Lateral interactions: size does matter.

Usually a high-contrast, co-local mask increases contrast threshold (inhibition). Interestingly, a laterally displaced mask (flanker) can facilitate contrast detection (Vision Research 33 (1993) 993; 34 (1994) 73). When spatial scaling of these flanker effects was implied, stimulus bandwidth was confounded with spatial frequency (lambda(-1)). Under conditions where at lower spatial frequencies, the size (standard deviation, sigma) of the Gabor patch was smaller (sigma<lambda) than higher spatial frequencies (sigma=lambda), the effect appeared scale invariant. We replicated the original results for all conditions. However, when Gabor size was fixed (sigma=lambda), facilitation changed with spatial frequency (range 2--13 cycles/deg). When Gabor size was varied (sigma=0.5-2 lambda), usually the combination of larger patch sizes and lower spatial frequencies caused inhibition. We were unable to find any conditions that demonstrated spatial scaling. The size, both lambda and sigma, of both stimulus and flankers, influenced contrast threshold. Also, facilitation reduced as contrast of the flankers was reduced to detection threshold. Some facilitation was apparent with sub-threshold flankers. These results need to be reconciled with current models of lateral interactions.

Adult↗