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P Goolkasian

Publications and source records attributed to P Goolkasian.

14 recordsLinked to original sources
PubMed1994

Size scaling and its effect on letter detection.

Two ways of scaling letter size across eccentricity were investigated in a choice reaction time (CRT) task. Experiments 1 and 2 tested cortical magnification theory (M-scaling), while Experiment 3 used scaled sizes drawn from Anstis's regression formula (A-scaling). Experiment 4 compared both scaling techniques, together with the effect of exposure duration and the absolute size of the foveal letter. Results showed that scaling effectiveness improved when large rather than small foveal letters were used. A-scaling with a large foveal letter provided a good fit for the data at parafoveal locations, but underestimated the letter sizes needed at large eccentricities. M-scaling with a large foveal letter size produced CRTs that were independent of eccentricity. Exposure duration did not substantially affect performance.

Fixation, Ocular↗
PubMed1990

Letter identification and lateral masking in dyslexic and average readers.

Lateral masking and letter identification in dyslexic and average readers were investigated with a methodology that corrected for some of the weaknesses of the Geiger and Lettvin studies (1986, 1987). Target letters were presented alone or embedded within three-letter arrays at retinal locations from 0 degrees to 15 degrees to the right or left of a fixation point. A foveal letter, which was the same as or different from a target letter, appeared as a distractor, and comparisons were made between scaled and unscaled stimuli. Dyslexic readers were found to be better than average readers at detecting scaled letters embedded in an array in some of the peripheral locations tested. Unlike the results of Geiger and Lettvin, however, this finding of better letter detection in the periphery by dyslexics was limited to selected conditions of the study. Reading groups were also found to differ in responding to the foveal distractor in the letter task. Detection of letters by average readers was affected by the type of distractor, but this variable was not found to influence the dyslexic readers. These findings suggest some differences between dyslexic and average readers in attention to stimuli presented at multiple locations in the visual field.

Adult↗
PubMed1987

Ambiguous figures: role of context and critical features.

Context and attention to critical features as factors in determining the perceptual organization of ambiguous figures were investigated in the present two studies. In the first study, a fixation point directed attention to a critical or to a neutral feature of an ambiguous figure. Placement of the fixation point on different features of an ambiguous figure did not affect the figure-ground organization of the figure, but it did influence the speed of the identification response. In the second study, presentation of an ambiguous figure was preceded by a biased figure or by features of the figure. Results indicated that the interpretation of the ambiguous figure was overwhelmingly influenced by the advanced presentation of a biased drawing but only slightly influenced by the advanced presentation of a critical feature. These findings support analysis-by-synthesis (Neisser, 1967) as an explanation of the perception of ambiguous figures over other contemporary attention theories.

Attention↗
PubMed1984

Picture-digit differences in processing clock times.

Clock times displayed as digits and as clockfaces were used as stimuli in a series of experiments that tested the hypothesis that a common numerical code was used for processing clock times. Whether the task involved reading times or making comparative judgments of early/late or same/different, digits were always processed faster than clockfaces . The size of the format effect varied, however, with the processing demands of the task and with times at specific locations on the clockface . Also, automatic processing of times presented as clockfaces interfered with comparative judgments made with digits, but digital distractors were not found to interfere with judgments made to times as clockfaces . The findings are discussed within the context of picture-word differences in rate of access to articulatory and semantic codes. Conclusions are also made regarding the relative efficiency of displaying times digitally and in the form of clockfaces .

Attention↗
PubMed1981

Retinal location and its effect on the processing of target and distractor information.

Two experiments were conducted to study the perceptual facilitation and inhibition that occurs between foveal and parafoveal or peripheral regions of the eye. Experiment 1 used a Stroop task to compare color detection latencies of foveal and parafoveal targets. The target and distractor components of the Stroop stimuli were separated and presented with varied stimulus onset asynchronies. Experiment 2 used a Stroop-like task to replicate and extend the findings into the visual periphery. Subjects were found to process foveally presented distractor information while attending to targets presented in parafoveal or peripheral regions of the eye. Distractor information that was incompatible was suppressed while compatible information was used to facilitate target processing. When the targets were presented foveally along with the distractor information, subjects appeared to automatically process the distractor information. The findings are discussed within the framework of past studies that presented subjects with competing tasks across retinal location. The implications of these findings to a two-process theory of attention are also considered.

Attention↗
PubMed1980

Processing of visually presented clock times.

The encoding and representation of visually presented clock times was investigated in three experiments utilizing a comparative judgment task. Experiment 1 explored the effects of comparing times presented in different formats (clock face, digit, or word), and Experiment 2 examined angular distance effects created by varying positions of the hands on clock faces. In Experiment 3, encoding and processing differences between clock faces and digitally presented times were directly measured. Same/different reactions to digitally presented times were faster than to times presented on a clock face, and this format effect was found to be a result of differences in processing that occurred after encoding. Angular separation also had a limited effect on processing. The findings are interpreted within the framework of theories that refer to the importance of representational codes. The applicability to the data of Bank's semantic-coding theory, Paivio's dual-coding theory, and the levels-of-processing view of memory are discussed.

Discrimination Learning↗
PubMed1978

Eye movements and a dynamic stimulus situation.

Two experiments were conducted to investigate performance with and without voluntary eye movements in a dynamic stimulus situation. Experiment I used a combined tracking and prediction task. Level of training, complexity of the signal, and visual region sampled were the variables of interest. Experiment II manipulated the same variables in only the prediction task. Thus, the amount of attention allotted to the prediction task was varied between experiments. The d' measure indicated that under peripheral vision instructions accuracy on the prediction task was the same as under foveal vision instructions provided that: (1) the level of task complexity was low, (2) the subjects were well trained, and (3) only the prediction task was performed, or in the dual task situation only visual regions near the fovea were sampled. All other combinations of the variables resulted in a lower performance scores under peripheral vision instructions. Results are interpreted within the framework of current theories of the functional visual field.

Eye Movements↗
PubMed1978

Reading and detecting color-word stimuli presented at various retinal locations.

Four experiments, using a total of 70 male and female undergraduates, examined the speed and accuracy of reading and detection responses to color-word stimuli presented at retinal locations from the center out to 6 degrees in the right and left visual fields. Reading and detection responses were found to interact with retinal location. For stimuli presented at the farther retinal location, detection responses were quicker and more accurate than reading responses, but the reverse occurred with foveally presented stimuli. The Stroop phenomenon was present in the detection data and was found to be diminished with parafoveal presentation of the stimulus materials. These findings support the peripheral search guidance process of Hochberg's model of reading and provide added evidence of processing variations across retinal location.

Color Perception↗