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Biomedical subjects

G R Loftus

Publications and source records attributed to G R Loftus.

At least 19 recordsLinked to original sources
PubMed2000

MATLAB and graphical user interfaces: tools for experimental management.

MATLAB is a convenient platform for the development and management of psychological experiments because of its easy-to-use programming language, sophisticated graphics features, and statistics and optimization tools. Through implementation of the Brainard-Pelli Psychophysics Toolbox, the MATLAB user gains close temporal and spatial control over the CRT, while retaining the simplicity of an interpreted language conductive to rapid program development. MATLAB's abilities can be further utilized through easily programmable graphical user interfaces (GUIs). We illustrate how a GUI can serve as a powerful and intuitive tool for organizing and controlling all aspects of a psychological experiment, including design, data collection, data analysis, and theory fitting.

Computer Graphics↗
PubMed2000

Accounts of the confidence-accuracy relation in recognition memory.

Confidence and accuracy, while often considered to tap the same memory representation, are often found to be only weakly correlated (e.g., Bothwell, Deffenbacher, & Brigham, 1987; Deffenbacher, 1980). There are at least two possible (nonexclusive) reasons for this weak relation. First, it may be simply due to noise of one sort or another; that is, it may come about because of both within- and between-subjects statistical variations that are partially uncorrelated for confidence measures on the one hand and accuracy measures on the other. Second, confidence and accuracy may be uncorrelated because they are based, at least in part, on different memory representations that are affected in different ways by different independent variables. We propose a general theory that is designed to encompass both of these possibilities and, within the context of this theory, we evaluate effects of four variables--degree of rehearsal, study duration, study luminance, and test luminance--in three face recognition experiments. In conjunction with our theory, the results allow us to begin to identify the circumstances under which confidence and accuracy are based on the same versus different sources of information in memory. The results demonstrate the conditions under which subjects are quite poor at monitoring their memory performance, and are used to extend cue utilization theories to the domain of face recognition.

Cognition↗
PubMed1999

A front end to a theory of picture recognition.

We describe the results of four picture-recognition memory experiments in which we systematically manipulated four variables: stimulus duration, stimulus contrast, the duration of a blank gap between successive presentations of the same stimulus, and the presence or absence of a noise mask that immediately followed stimulus offset. The patterns of obtained data confirmed a simple extension of a theory previously used to account for digit recall data. This theory consists of a low-pass linear-filter front end that generates a sensory response from the physical stimulus, followed by an information-sampling process whose instantaneous sampling rate is based in part on the sensory response magnitude. The data confirm both qualitative and quantitative theoretical predictions, some of which were previously untestable in digit recall tasks because of ceiling effects that were not present in our picture-recognition tasks. We describe the role of our theory within the broader family of picture-memory theories, and we briefly discuss our theory's unification of two salient facets of visual behavior: information acquisition on the one hand, and phenomenological appearance on the other hand.

Contrast Sensitivity↗
PubMed1998

On the relations among different measures of visible and informational persistence.

We report research designed to accomplish two goals. We first consider the question, raised by Coltheart (1980) and others, of whether three measures of visible and informational persistence--performance in temporally integrating two successively presented stimuli, subjective rating of the degree to which two successively presented stimuli appear to constitute a single or a dual temporal event, and partial-report performance--all measure the same underlying mental entity. We answer this question using a superset of dissociation logic called state-trace analysis (Bamber, 1979), and within the context of a systematic empirical foundation consisting of seven closely related experiments. Our second goal is to extend and apply a theory to data acquired from our seven experiments and also to data reported by other investigators. This theory, which has been confirmed in a variety of paradigms (see Busey & Loftus, 1994) assumes that (1) the initial stages of the visual system act as a low-pass linear filter which operates on a stimulus temporal waveform to produce a sensory response; (2) instantaneous rate of acquiring information from the stimulus is jointly proportional to sensory-response magnitude and proportion of as-yet-to-be-acquired stimulus information; (3) partial-report performance is determined by total amount of acquired information; (4) the probability that two events are perceived as contemporaneous is determined by the temporal correlation of their respective information-acquisition rate functions (which is similar to a suggestion by Dixon & Di Lollo, 1994); and (5) temporal integration is successful to the degree that the two temporal events are perceived as contemporaneous. This theory was highly successful in accounting for our and other investigators' temporal-integration and completeness-rating data, and was moderately successful in accounting for partial-report data. We discuss the degree to which our three persistence measures can be united within the context of our theory; we comment on the distinction between objective and subjective measures of visible persistence; and we address the decades-old question: "What is persistence good for?"

Humans↗
PubMed1998

Binocular information acquisition and visual memory.

Mechanisms underlying the binocular combination of visual information were investigated within the context of a visual information acquisition theory proposed by Loftus, Busey, and their colleagues (e.g., as described by T.A. Busey & G. R. Loftus, 1994). A central assumption of the theory is that of a sensory threshold, which engenders an information loss such that information processing subsequent to the threshold is assumed to occur only when the magnitude of a sensory representation triggered by the stimulus exceeds the threshold. The presumed sensory threshold may be situated prior to or subsequent to the point at which the information from the two eyes combines. The location of this threshold was investigated in 3 experiments that provided conclusions about the location of the sensory thresholds and the mechanisms of binocular combination. It is concluded that a linear summation mechanism, an independent sampling information acquisition model, and both pre- and postcombinatorial sources of information loss are required to account for the data.

Humans↗
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↗