PubMed · 5661779
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J D Mollon. Fixation and perception.. https://doi.org/10.1080/713818090
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Exact functional testing in macular diseases still presents a challenge for the ophthalmologist in detecting both small (para)central scotomas and changes in fixation habits. The recent development of scanning laser ophthalmoscopy has enabled functional testing with simultaneous observation of the fundus. In addition to automatic static threshold fundus perimetry, kinetic fundus-controlled perimetry and special fixation tasks can be applied. This method also allows the examination of reading performance combined with the exact observation of fixation and has been increasingly integrated into clinical routine. This allows more exact observations concerning macular function for diagnostic purposes, in evaluating new treatment methods, and as expertises in simulation or aggravation in patients with macular diseases.
Theories on visual search differ substantially with respect to the relationship they assume between localization and identification processes. The aim of the present study was to rigorously compare the alternative theoretical notions on how localization and identification processes are related. In two experiments, participants searched for a target with a unique line orientation among distractors containing another orientation. Localization and identification performance were measured in combination, as function of display size and target eccentricity. To compare the alternative theories, formal binomial models were developed and compared with respect to their goodness of fit to the individual data. The formal analyses showed that the model assuming identification processes to be conditioned on localization processes provided the best fit to the individual data. Furthermore, maximum likelihood estimates of the parameter corresponding to identification processes were differently affected by display size than identification performance was. The results were discussed in terms of their implication for current theories on visual search.
This paper reports an analysis of saccades made during a task of visual search for a colour shape conjunction. The analysis concentrates on the saccade following the first saccade, thus complementing an earlier paper where the first saccades were analysed. The further analysis addresses the issue of what information might be held in trans-saccadic memory. As with the first saccade, incorrect second saccades tend to fall on distractors sharing one feature with the target. The proximity of the target to the fixation location immediately prior to the saccade is a very significant determinant of whether the saccade will reach the target. The results lead to the conclusion that in the majority of cases, choice of saccade destination is made afresh during each fixation with no carry-over from the previous fixation. However, in a small number of cases, second saccades are made after extremely brief fixation intervals. Although these saccades show a similar probability of reaching the target as those following longer fixations, it is argued that this sub-set of saccades are pre-programmed at the time of the preceding saccade.