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Biomedical subjects

G M Long

Publications and source records attributed to G M Long.

At least 55 records · Page 3Linked to original sources
PubMed1982

The case for peripheral persistence: effects of target and background luminance on a partial-report task.

The effects of varying target and background luminances were examined on a partial-report task of iconic memory. Experiment 1 demonstrated that with a dim preexposure and postexposure field, varying target luminance has a marked effect on performance. Increased luminance results in significantly longer iconic storage. In Experiment 2 performance on the task was determined as the background luminance was systematically increased. It was found that not only is the duration of iconic storage reduced by increasing background luminance but changes in target luminance have progressively less of an effect as background luminance increases. These results are discussed in terms of the known response properties of cone and rod photoreceptors and their potential contribution to iconic memory. Finally, possible reasons for discrepancies with other iconic memory studies are detailed.

Adult↗
PubMed1982

Rod persistence on a partial-report task with scotopic and photopic backgrounds.

Two experiments were undertaken to demonstrate the participation of the rod system under certain stimulus conditions on the partial-report task of iconic memory. In Experiment 1, scotopically matched letter arrays of differing wavelength produced equivalent partial-report superiority but only if relatively large letters and a long cue delay were employed. In Experiment 2, variable photopic backgrounds were employed in contrast to the constant dark background used in the first experiment. For constant luminance targets, photopically matched red and blue-green backgrounds of 5 ftL (15.9 cd/m2) did not produce equivalent partial-report performance. Partial-report superiority was evident at much longer cue delays with the red background. This was attributed to the minimal stimulation of the rod system by this long wavelength background. However, if an intense adaptation field that saturated the rod system were interposed between stimulus trials, the photopically matched backgrounds then produced equivalent partial-report performance at all cue delays.

Color Perception↗
PubMed1981

Multiple representations of the same reversible figure: implications for cognitive decisional interpretations.

Observations are reported with the side-by-side presentation of rotating Necker cubes and other well-known reversible (ambiguous) figures. The fact that the two representations can be seen in the opposite direction of rotation, or perspective, at the same time is regarded as a serious difficulty for the cognitive or decisional interpretations of the spontaneous alternations in these figures. It is suggested that separate and fatiguable cortical 'channels' are a more likely basis for the dual-presentation effect than multiple decisional or attentional processes. The relationship between this proposal and recent research consistent with the visual system as a multichannel processor is noted.

Cognition↗
PubMed1980

The retinal basis of iconic memory: Eriksen and Collins revisited.

The parameters of luminance, duration, wavelength, and interstimulus interval (ISI) were varied on the successive-field task first employed by Eriksen and Collins in 1967 and 1968. This task requires observers to combine visually the information presented in two brief successive presentations for successful trigram recognition. The results of the luminance and duration manipulations indicate that as stimulus energy is increased, iconic memory also increases. The wavelength and ISI manipulations reveal that performance at 20 msec ISI reflects cone (photopic) sensitivity but that performance at 250 msec ISI reflects rod (scotopic) sensitivity. These findings are interpreted in support of the retinal conception of iconic memory, with the cones providing a very transient icon and the rods providing the bulk of the persistence.

Female↗
PubMed1979

Spare the rod and spoil the icon.

Short-term visual storage was investigated with a successive field paradigm, so that correct performance depended upon combining visual information from two targets that were never on simultaneously. In the first two experiments, the stimuli consisted of two slides, each containing a 10' red dot on a gray surround, and separated by an interstimulus interval (ISI) from 20 to 400 msec. Subjects had to determine if the dots were vertically or horizontally aligned. In Experiment 1, the stimuli had either no contrast for the rods or no luminance contrast for the cones or high contrast. At short ISIs the cone contrast determined performance, whereas at long ISIs the rod contrast determined performance. In fact, when the dots were invisible to the rods, the task was impossible for long ISIs. In Experiment 2, performance was compared for zero log rod contrast and for small departures from zero. Even a small departure from zero log rod contrast resulted in above-chance performance. In Experiment 3, the stimuli were luminous rectangles and the task was to decide whether or not a 4' spatial gap was present between the two successively presented rectangles. Wavelength, luminance, and ISI were varied under both photopic and scotopic adapting conditions. The result was that the rods performed the task for ISIs of 150 msec or longer under scotopic conditions and under the photopic conditions that we were able to test. The results of the experiments taken together are consistent with the hypothesis that the cone icon is short, whereas the rod icon is robust and long lasting.

Color Perception↗
PubMed1978

The unspecified role of cones and rods in grating detection: a theoretical note.

Detection and resolution thresholds for two 50 ms square-wave gratings (1.5 and 6.7 cps) were determined as a function of background luminance. Results indicated differential cone and rod involvement in resolution of the two targets at low background levels. Implications for other studies employing similar stimuli in terms of retinal inhomogeneity were suggested.

Luminescent Measurements↗