Biomedical subjects

K M Joffe

Publications and source records attributed to K M Joffe.

6 recordsLinked to original sources

PubMed1998

Response times and eye movements in feature and conjunction search as a function of target eccentricity.

In four experiments, saccadic eye movements, reaction times (RTs), and accuracy were measured as observers searched for feature or conjunction targets presented at several eccentricities. A conjunction search deficit, evidenced by a large eccentricity effect on RTs, accuracy, and number of saccades, was seen in Experiments 1A and 1B. Experiment 2 indicated that, when saccades were precluded, there was an even larger eccentricity effect for conjunction search targets. In Experiment 3, practice in a conjunction search task allowed both RT and number of saccades to become independent of eccentricity. Additionally, there was evidence of feature-based selectivity in that observers were more likely to fixate distractors that had the same contrast as the target. Results are consistent with the view that the oculomotor and attentional systems are functionally linked and provide constraints for models of visual attention and search.

Attention↗

PubMed1997

Motion coherence perimetry in glaucoma and suspected glaucoma.

Motion direction sensitivity in glaucoma patients, glaucoma suspects and controls was assessed perimetrically at 22 visual field locations using small random dot kinematograms and a motion coherence task. For foveal stimulus presentations, mean motion coherence sensitivity was normal in both patient groups. However, nearly all glaucoma patients and about half of glaucoma suspects (all with normal visual fields as assessed with static perimetry) had some deficit of motion sensitivity. These were most pronounced and most prevalent in the superior field at 15 and 21 deg eccentricity. Glaucoma appears to produce a reduction in the normal integrative visual function necessary for the perception of global motion in textured displays and this disruption is non-uniformly distributed across the visual field.

Female↗

PubMed1995

Texture segmentation as a function of eccentricity, spatial frequency and target size.

Two experiments examined the role of fundamental spatial frequency, target area and retinal eccentricity in texture segmentation. In Experiment 1, a backward-masked target comprising lines oriented orthogonally to the surround was briefly presented at the fovea, and at eccentricities ranging from 2.55 to 7.63 deg. Reaction time and accuracy were better when targets were presented at non-foveal locations. In Experiment 2, eccentricity effects were examined when both spatial frequency and target area were varied. Accuracy was highest and RT fastest at near-peripheral, not foveal locations. The eccentricity corresponding to optimal performance was related inversely to spatial frequency. Results suggest that the near periphery is more adept than the fovea at the early processing which underlies rapid texture segmentation.

Adult↗

PubMed1995

Preferential processing of target features in texture segmentation.

In five experiments, observers were required to detect a texture target and/or identify the orientation of elements composing target and nontarget regions. They were significantly worse at discerning the orientation of nontarget regions than at detecting target presence (Experiment 1). On the other hand, accuracy of identifying target orientation was found to be near 100% (Experiment 2). When observers were required only to identify surround orientation (Experiment 3), accuracy was diminished on target-present trials relative to that on target-absent trials. The superiority of target processing and the interference produced by target presence on surround processing were demonstrated in unpracticed observers (Experiment 4). In Experiment 5, it was found that information regarding target presence is available before information regarding feature values of the target. These findings are consistent with a model of visual attention and search that incorporates a fast generalized difference operator and a slower feature comparison process.

Adult↗

PubMed1994

Age differences in the useful field of view: an eye movement analysis.

Age differences in the useful field of view (UFOV) were examined by asking younger (mean age = 24 years) and older (mean age = 64 years) observers to search for two oriented line targets. These targets were presented at eccentricities ranging from 4 degrees to 14 degrees, and were embedded in either no distractors, homogeneous distractors, or heterogeneous distractors. Eye movements were recorded, along with reaction time (RT) and accuracy. The eye movement data indicated that older observers had more difficulty locating peripheral targets, particularly when they were embedded in heterogeneous distractors. Furthermore, the greater effects of eccentricity and distractor type found in the RT's of older adults were eliminated when age differences in saccade number were partialled out. These findings suggest that age differences in search are largely attributable to factors other than selective attention.

Adult↗

PubMedDate not supplied

Age, target-distractor similarity, and visual search.

Younger and older adults were asked to find a single target in both feature- and conjunction- search conditions. Display size varied between 2 and 8 items, and target-distractor similarity ranged from relatively low to high levels. The accuracy data indicated that older adults had particular difficulty finding targets in high-similarity conjunction-search displays containing a large number of distractors. The reaction time (RT) analyses found larger age deficits in many of these same conditions. For both groups, predictions of conjunction search based on Treisman and Sato's additive model (Journal of Experimental Psychology: Human Perception and Performance, 1990: 16, 459-478) departed significantly from actual performance. The RT data of older observers were, in large part, predicted as a simple linear function of the young adults' data. These results are discussed with respect to age differences in selective attention, generalized slowing, and an age-related loss in search efficiency.

Adolescent↗