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G R Loftus

Publications and source records attributed to G R Loftus.

At least 19 recordsLinked to original sources
PubMed1994

A theory of visual information acquisition and visual memory with special application to intensity-duration trade-offs.

We describe a theory of memory for visual material in which the visual system acts as a linear filter operating on a stimulus to produce a function, a(t), relating some sensory response to t (the time since stimulus onset). Stimulus information is acquired at a rate proportional to the product of the magnitude by which a(t) exceeds some threshold, and the amount of as-yet-unacquired information. Recall performance is assumed to equal the proportion of acquired information. The theory accounts for data from 2 digit-recall experiments in which stimulus temporal waveform was manipulated. We comment on the theory's account of the relation between 2 perceptual events: the phenomenological experience of the stimulus, and the memory representation that accrues from stimulus presentation. We assert that these 2 events, although influenced by different variables, can be viewed as resulting from 2 characteristics of the same sensory-response function.

Female↗
PubMed1994

Sensory and cognitive components of visual information acquisition.

The authors describe a theory of visual information acquisition and visual memory. The theory has 2 major components. First, the visual system's initial sensory response to a short-duration, low-contrast stimulus is generated by a linear, low-pass temporal filter that operates on the stimulus's temporal waveform. Second, information is acquired from a stimulus through an independent-sampling process whose sampling rate at time t following stimulus onset is jointly proportional to (a) the magnitude by which the sensory response exceeds some threshold and (b) the proportion of still unacquired information. The theory was successfully tested in 5 variants of a digit recall task in which temporal waveform of the stimulus was systematically manipulated. In a final experiment, the theory simultaneously accounted for performance in detection and identification tasks. Implications for visual information processing, low-contrast detection, and binocular combination of information are discussed.

Cognition↗
PubMed1993

Providing a sensory basis for models of visual information acquisition.

Our major goal is to account for some simple digit-recall data with a theory that integrates two models from two scientific traditions. The random-sampling model, founded in the memory and attention literature, holds that (1) stimulus features are randomly sampled throughout the course of stimulus presence and (2) proportion correct recall is equal to the ratio of sampled features to total features. The linear-filter model, founded in the vision and sensation literature, holds that the initial stages of the visual system act as a low-pass temporal filter on the input stimulus, resulting in a time-varying sensory response in the nervous system. We report two experiments in which a variable-duration, masked, four-digit string had to be immediately recalled. Experiment 1 was designed principally to replicate past data confirming the basic random-sampling model. Like others, we were able to confirm the model only by endowing it with an additional processing-delay assumption: that feature sampling does not begin until the stimulus has been physically present for some minimal duration. Experiment 2 was an extension of Experiment 1 in which the target stimulus was preceded, 250 msec prior to its onset, by a 50-msec pre-presentation of the same stimulus called a prime. The Experiment 2 results allowed the following conclusions. First, the initial processing delay found in Experiment 1 is immutably tied to stimulus onset; that is, if there are two stimulus onsets, separated even briefly in time, there are two associated processing delays. Second, processing rate is essentially unaffected by the prime's presentation. Third, being presented with a 50-msec prime is equivalent, in terms of memory performance, to increasing unprimed stimulus duration by approximately 30 msec; the prime can thus said to be worth 30 msec of additional exposure duration. This third conclusion seems superficially paradoxical, in the sense that one would expect that having seen a 50-msec prime would be equivalent to increasing exposure duration by at least the same 50 msec. However, both the initial processing delays and the 30-msec prime's worth are natural consequences of our theory that conjoins the random-sampling model with the linear-filter model.

Adult↗
PubMed1992

On the time course of perceptual information that results from a brief visual presentation.

A briefly presented visual stimulus engenders an available-information function that lags behind the physical stimulus. We report two experiments that focus on the iconic-decay portion of this function, which falls to 0 over a 200-300 ms period following stimulus offset. In each experiment, to-be-reported digit strings were shown for varying durations followed by a noise mask at varying poststimulus intervals. We found the shape of the performance curve relating digit-report probability to stimulus exposure duration to be independent of stimulus-mask interstimulus interval. This finding is consistent with the proposition that the iconic-decay function's shape is independent of stimulus duration and allows us to identify this shape. We rejected exponential iconic decay for 6 of 8 observers; however, all observers' decay functions could be adequately fit by gamma decay, a generalization of exponential decay.

Adult↗
PubMed1991

Eye fixations and memory for emotional events.

Subjects watched either an emotional, neutral, or unusual sequence of slides containing 1 critical slide in the middle. Experiments 1 and 2 allowed only a single eye fixation on the critical slide by presenting it for 180 ms (Experiment 1) or 150 ms (Experiment 2). Despite this constraint, memory for a central detail was better for the emotional condition. In Experiment 3, subjects were allowed 2.70 s to view the critical slide while their eye movements were monitored. When subjects who had devoted the same number of fixations were compared, memory for the central detail of the emotional slide was again better. The results suggest that enhanced memory for detail information of an emotional event does not occur solely because more attention is devoted to the emotional information.

Adult↗
PubMed1990

Learning-forgetting independence, unidimensional memory models, and feature models: comment on Bogartz (1990).

In his recent articles, Bogartz offered a definition of what it means for forgetting rate to be independent of degree of original learning. He showed that, given this definition, independence is confirmed by extant data. Bogartz also criticized Loftus's (1985b) proposed method for testing independence. In this commentary, we counter Bogartz's criticisms and then offer two observations. First, we show that Loftus's horizontal-parallelism test distinguishes between two interesting class of memory models: unidimensional models wherein the memory system's state can be specified by a single number and multidimensional models wherein at least two numbers are required to specify the memory system's state. Independence by Loftus's definition is implied by a unidimensional model. Bogartz's definition, in contrast, is consistent with either model. Second, to better understand the constraints on memory mechanisms dictated by the mathematics of the models under consideration, we develop a simple but general feature model of learning and forgetting. We demonstrate what constraints must be placed on this model to make learning and forgetting rate independent by Loftus's and by Bogartz's definitions.

Humans↗
PubMed1989

The phenomenology of spatial integration: data and models.

A briefly presented visual stimulus followed by darkness seems to persist beyond its physical offset. We are concerned here with the relation between two characteristics of this visible persistence: first, its phenomenological resemblance to the stimulus that spawned it and second, its usefulness as a basis for integrating visual stimuli that are separated in time. We describe two experiments using a task in which two halves of a visual stimulus were presented successively and observers reported how complete the stimulus appeared to be. Stimuli appeared less complete with increases in both the duration of the interval intervening between presentation of the two halves and the duration of the initially presented stimulus half. This data pattern is similar to that obtained in tasks in which spatial integration of two temporally disparate stimuli is necessary for correct responding. On the basis of this similarity, we argue that phenomenological appearance and ability to integrate stimuli over time are two facets of the same perceptual events. We describe a formal model to account for these and other data.

Adult↗
PubMed1989

Effects of semantic priming on visual encoding of pictures.

We investigated the effects of semantic priming on initial encoding of briefly presented pictures of objects and scenes. Pictures in four experiments were presented for varying durations and were followed immediately by a mask. In Experiments 1 and 2, pictures of simple objects were either preceded or not preceded by the object's category name (e.g., dog). In Experiment 1 we measured immediate object identification; in Experiment 2 we measured delayed old/new recognition in which targets and distractors were from the same categories. In Experiment 3 naturalistic scenes were either preceded or not preceded by the scene's category name (e.g., supermarket). We measured delayed recognition in which targets and distractors were described by the same category names. In Experiments 1-3, performance was better for primed than for unprimed pictures. Experiment 4 was similar to Experiment 2 in that we measured delayed recognition for simple objects. As in Experiments 1-3, a prime that preceded the object improved subsequent memory performance for the object. However, a prime that followed the object did not affect subsequent performance. Together, these results imply that priming leads to more efficient information acquisition. We offer a picture-processing model that accounts for these results. The model's central assumption is that knowledge of a picture's category (gist) increases the rate at which visual information is acquired from the picture.

Attention↗
PubMed1986

Information-acquisition rate, short-term memory, and cognitive equivalence: reply to Sperling.

The effect of stimulus luminance on visual information acquisition depends on the duration for which the stimulus is displayed. In this reply, three duration regions are described, and the accounts of luminance effects provided by Loftus (1985d) and Sperling (1986) are compared for each region. Of particular interest is why different combinations of duration and luminance produce equal performance levels. Two possibilities are considered: first, equal performance may be a logical consequence of equivalent cognitive states and second, equal performance may be a coincidental consequence of different cognitive states. I suggest that equal performance following relatively short durations results from equivalent cognitive states, whereas equal performance following longer durations results from different cognitive states.

Cognition↗
PubMed1985

How much is an icon worth?

We report a new technique for assessing the amount of information extracted from the icon that follows a briefly presented picture. The problem of how to measure such information was formulated in terms of how much physical exposure of a picture an icon is worth. Consider two types of stimulus presentations, each with a base duration of d ms. The first is a d-ms picture followed by an icon, and the second is a d + a-ms picture not followed by an icon. How large does a have to be so that equivalent amounts of information are extracted in the two cases? To answer this question, we showed people pictures and later tested their memory for the pictures. We found that the physical exposure duration needed to reach a particular level of performance was approximately 100 ms longer when an icon was not permitted versus when the icon was permitted. This value was independent of the base duration and the luminance of the picture. Moreover, the same value was obtained using three different kinds of memory test and four different sets of pictures. We conclude that an icon is worth approximately 100 ms of additional physical exposure duration. A reasonable explanation for this robust equivalence between icon and stimulus is that the same encoding processes are responsible for extracting information from the icon and from the physical stimulus. Therefore, any variable that affects these encoding processes must affect extraction of information from the icon and the physical stimulus in an identical manner. This prediction was confirmed for one such variable, picture luminance.

Figural Aftereffect↗
PubMed1985

Size illusion, distance illusion, and terrestrial passage: comment on reed.

Two assumptions of Reed's (1984) terrestrial passage theory are questioned. First, Reed assumes that the moon's failure to increase in visual subtense while elevating is accounted for strictly by perceptual distancing. This allows a formal account of the moon distance illusion, but at the expense of a compelling explanation of the moon size illusion. Second, in order to explain the distance illusion, Reed assumes that all objects, regardless of their perceived altitude, are perceived to start from a common point at the horizon. Several alternative application of Reed's terrestrial-passage foundation to the actual illusions are suggested.

Astronomical Phenomena↗
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↗