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Biomedical subjects

H H Greene

Publications and source records attributed to H H Greene.

8 recordsLinked to original sources
PubMed2001

Eye movements and familiarity effects in visual search.

Familiarity with the distractors around an unfamiliar target facilitates visual search. Three Experiments examined whether the effect occurs because fixations are (a) shorter and fewer, (b) shorter, but more abundant, (c) equally long, but fewer, or (d) longer, but fewer when distractors are familiar. Results indicated comparably long, but fewer fixations when distractors are familiar. Hence, the theory that unfamiliar distractors need longer processing is discounted. In a fourth Experiment, a gaze-contingent moving window paradigm was used to control peripheral processing. Results revealed a wider span of effective processing for familiar distractors. A hypothesis based on low-level physiological processes is introduced to account for the familiarity effect.

Adolescent↗
PubMed2001

Eye-movement control in direction-coded visual search.

Subjects searched for a target among distractors which were arranged randomly or such that each distractor provided information about the relative position of a target. Trials were presented either in a blocked design (so that the subjects knew a priori the contextual information in the display) or in a mixed design. When the distractors provided information about target position, there were (i) shorter manual RTs, (ii) fewer fixations made in search of the target, (iii) longer mean fixation durations, (iv) shorter initial fixation durations, (v) shorter mean gaze shifts, (vi) a smaller area of fixation dispersion, and (vii) a greater percentage of optimally directed saccades. Except for gaze shifts, the results were uninfluenced by whether or not there was a blocked or a mixed presentation. The results of the study suggest that despite noise in the search mechanism, fixation durations were adjusted to process directly the currently fixated element(s).

Adolescent↗
PubMed2000

Amodal completion and localization.

In a three-line vernier acuity task, a central line was localized between two aligned line segments. Accuracy did not improve when the segments formed a unified amodally completed percept. In a two-line vernier acuity task, a line was localized below a target line placed next to a physically segmented flank stimulus. Shifts in mean points of subjective equality suggested that amodally completed segments influenced localization. Previous conflicting findings are explained by a representation that is available early to influence perceived alignment. However, position tuning is poor. This representation may be realized physiologically by interpolation responses between amodally completed segments.

Adult↗
PubMed1999

Temporal relationships between eye fixations and manual reactions in visual search.

Observers freely searched for, and manually responded to, the presence of a target in multistimulus displays. The stimuli were presented on a cinema screen such that each display subtended a large visual angle to encourage the use of eye movements. Times taken to initially fixate the target (T1Fs) were compared to manual response times (MRTs). The results of two experiments were qualitatively similar, despite different levels of difficulty between them. MRTs were a linear function of T1Fs, but only when fixations did not occur very early after the onset of the stimulus display. When fixations were made very soon after the onset of the display, T1Fs were independent of MRTs. The findings were described within the framework of a one-way synchronization model which was modified to accommodate attention effects in visual search. Finally, the methodology provides a novel means of quantifying the contributions of eye movements to manual acknowledgements in real-world vision-guided tasks.

Adult↗
PubMed1997

Spatial interactions with real and gap-induced illusory lines in vernier acuity.

Vernier acuity for illusory line targets induced by gaps in a horizontal grating was measured in the presence of real and illusory flanks. In a 500 msec presentation forced choice task, observers judged the position of a comparison illusory line positioned 3 min arc below the target. The results show that illusory lines are capable of interacting with real lines in spatial localization. Thus, they provide psychophysical evidence for a common localization mechanism that supports real and illusory contour definitions. The results further show a sensitivity of the visual system to the contrast polarity of real lines. This sensitivity was absent for illusory lines. The present findings are discussed in terms of their relationship to physiological findings, and in terms of their potential to constrain computational models that account for illusory contour brightness.

Humans↗
PubMed1995

The effect of nearby luminance contrast polarity on color boundary localization.

The study measured the shift in apparent position of a color-defined target boundary as a function of the distance, luminance polarity and amount of contrast of a nearby luminance-defined flanking boundary. In general, the position of the target boundary shifted towards the flank with the attraction being somewhat greater for negative than positive polarity flanks, and for high compared to low contrast flanks. High contrast, negative polarity flanks resulted in greater attraction at 3.69 min arc separation. For low contrast flanks, the apparent shift in position of the target boundary depended on the polarity and position of the flank relative to the target. For example, for small separations ( < 3 min arc) flank polarity had little influence, while for larger separations ( > or = 3.69 min arc), negative polarity flanks exhibited attraction while positive polarity flanks began to show repulsion. The results support the notion that luminance and color processing may share a common representation for the localization of boundaries. Position judgments based on this representation appear to be influenced by the amount of luminance contrast in a nearby boundary.

Color Perception↗
PubMed1985

The ten-year malpractice experience of a large urban EMS system.

Malpractice is a recognized and growing problem for physicians and hospitals, but it is difficult to ascertain the risk of malpractice in the prehospital arena. Dade County, Florida (greater Miami), with a population of 1.7 million, currently is served by 339 certified paramedics. During the decade of 1972 to 1982, Dade County Fire Rescue handled 265,060 incidents; 16 claims were filed with the Risk Management Division of Dade County. The claims were produced by 11 incidents, which yields a rate of one per 24,096 incidents. The two greatest problems identified were inadequate record keeping and "gray zone" patients who do not fit any particular protocol.

Aged↗