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G R Loftus

Publications and source records attributed to G R Loftus.

27 records · Page 2Linked to original sources
PubMed1985

Picture perception: effects of luminance on available information and information-extraction rate.

In each of four experiments, complex visual stimuli--pictures and digit arrays--were remembered better when shown at high luminance than when shown at low luminance. Why does this occur? Two possibilities were considered: first that lowering luminance reduces the amount of available information in the stimulus, and second that lowering luminance reduces the rate at which the information is extracted from the stimulus. Evidence was found for both possibilities. When stimuli were presented at durations short enough to permit only a single eye fixation, luminance affected only the rate at which information is extracted: decreasing luminance by a factor of 100 caused information to be extracted more slowly by a factor that ranged, over experiments, from 1.4 to 2.0. When pictures were presented at durations long enough to permit multiple fixations, however, luminance affected the total amount of extractable information. In a fifth experiment, converging evidence was sought for the proposition that within the first eye fixation on a picture, luminance affects the rate of information extraction. If this proposition is correct and, in addition, the first eye fixation lasts until some criterion amount of information is extracted, then fixation duration should increase with decreasing luminance. This prediction was confirmed.

Attention↗
PubMed1984

Perceptual and conceptual masking of pictures.

We report an experiment in which target pictures, presented for 50 ms, were followed by masks. Two mask variables were implemented: mask luminance and amount of attention demanded by the mask. Luminance but not attention demand affected subsequent picture-memory performance when the mask followed the picture immediately; however, attention demand but not luminance affected performance when the mask was delayed by 300 ms following the offset of the picture. We conclude that qualitatively different processes are being carried out at 0 versus 300 ms following the offset of a 50-ms picture. We argue that these processes can profitably be viewed as perceptual processes, which operate on raw stimulus input, and conceptual processes, which operate on the output of perceptual processes.

Attention↗
PubMed1981

Tachistoscopic simulations of eye fixations on pictures.

In three picture recognition experiments, complex pictures were presented during a study phase, each presentation consisting of n sequential masked presentations and each presentation lasting d msec. This procedure was designed to mimic a series of eye fixations over a picture, but with number and duration of fixations under experimental control. With n held constant, subsequent recognition memory performance increased with increasing d up to 400 msec. With d held constant, performance increased with increasing n only to the degree that an additional presentation of a picture was used to fixate a novel portion of the picture. These results, and those of Loftus's 1972 experiment, suggest a model of picture encoding that incorporates the following propositions: (a) A normal fixation on a picture is designed to encode some feature of the picture. (b) The duration of fixation is determined by the amount of time required to carry out the intended feature encoding. (c) The more features are encoded from a picture, the better the recognition memory will be form the picture. Additionally, the results of the present experiments imply that the events that constitute encoding within a fixation proceed in a fixed, relatively immutable order.

Eye Movements↗
PubMed1980

The functional visual field during picture viewing.

In four experiments, pictures of complex, naturalistic scenes were shown, followed by a two-alternative forced-choice recognition test in which the targets and distractors differed in only a single, critical detail. Eye movements were recorded at the time of study in the first two experiments. In Experiment 1 we investigated eye movements during short initial exposure times and found that if the nearest fixation to the critical detail was further than about 2 degrees of visual angle, performance was no better than chance. Experiment 2 replicated Experiment 1 using longer exposure times and an expanded set of pictures. Performance was still found to decrease with increase in distance of the nearest fixation to the critical detail, but not quite to chance. In Experiments 3 and 4 we controlled where the subject's first fixation occurred using a prefixation point of light. The results indicated that the performance again decreases with increasing distance from the critical detail; however, performances did not fall completely to chance levels. In Experiment 4 a verbal recognition test was included, and overall performance was still slightly better than chance at extreme distances. It was concluded that some information is stored from the visual periphery during picture viewing.

Adult↗
PubMed1979

Encoding and use of detail information in picture recognition.

Subjects participated in a yes/no picture recognition experiment in which exposure time varied from 50 to 1,000 msec at the time of initial study. Following each study trial, half of the subjects, the detail at study and test (ST) group, reported whether they had observed a detail in the picture that they thought might help in subsequent recognition. The other half of the subjects, the detail at test only (T) group, did not attempt to name details during study. All of the subjects reported at the time of each test picture whether they were basing their yes/no recognition response on a specific detail in the picture or on the picture's general familiarity. The data provided strong support for a model which assumed that (a) there is a constant probability of encoding a detail during each successive unit of time at study and (b) a detail is named at test either if it was encoded at study or with some bias probability. ST subjects showed superior recognition memory performance relative to T subjects. Within the context of the aforementioned model, this superiority stems from two sources: ST subjects encode details at a faster rate than do T subjects and an encoded detail provided a better discriminative feature for ST subjects.

Discrimination Learning↗
PubMed1978

Cognitive determinants of fixation location during picture viewing.

This experiment involved the question of where human observers look in a picture. The results indicated that observers fixate earlier, more often, and with longer durations on objects that have a low probability of appearing in a scene (e.g., an octopus in a farm scene) than on objects that have a high probability of appearing (e.g., a tractor in a farm scene). These findings (a) imply a role of cognitive factors in peripheral visual processing and (b) suggest a possible relationship between the nature of information initially acquired from a picture and subsequent recognition memory for that picture.

Adolescent↗
PubMed1975

Two types of information in picture memory.

It is assumed that recognition memory for pictures is based on two types of information. The first is information about specific details in a picture. The process of encoding this type of information is identified with what N. H. Mackworth and others have termed looking at "informative areas" in pictures. The second informational component is designated as "general visual information." Two experiments were carried out investigating (a) the extent to which recognition responses to pictures are based on specific detail vs. general visual information, (b) whether the amount of specific detail information may be manipulated by varying the complexity of a target picture, and (c) the rate at which the two types of information are acquired. The results indicate that the rate of encoding specific details varies with the number of potential informative areas in a pictures and, given that a detail is encoded, memory performance is not substantially affected by target complexity, exposure time, or presence or absence of a mask.

Acoustic Stimulation↗