Biomedical subjects

G Chastain

Publications and source records attributed to G Chastain.

At least 19 recordsLinked to original sources

PubMed2001

Attentional capture with various distractor and target types.

Effects of nonpredictive distractors that involved changes in luminance, size, or shape were examined in three experiments. In Experiment 1, with two types of distractors (onsets and offsets), accuracy was better on trials when the distractor was near the location of either an offset or an onset target than on trials when the distractor was in a different location from that of the target, demonstrating attentional capture. Capture occurred both when the type of target (onset or offset) was blocked and therefore predictable and also when the type of target was mixed within blocks and therefore not predictable. Further experiments indicated that distractors captured attention even when the change to distractor did not create a new perceptual object. Neither a singleton-detection mode, nor a contingent involuntary orienting hypothesis, nor creation of a new object seems to explain all of these data adequately. Rather, capture may depend on a number of factors in the task.

Adolescent↗

PubMed1999

Attention effects of abrupt-onset precues with central, single-element, and multiple-element precues.

Endogenous and exogenous processes of attention have been inferred with different types of precues used in allocation of attention to a target location. In the present research, a comparison was made between the typical peripheral single-element precue (SEP), a central precue, and a multiple-element precue (MEP) in order to further understanding of the processes involved in allocation of attention. Two precues were used on each trial in these experiments. An abrupt-onset precue appeared with an SEP, an MEP, or a central precue and was followed 50 or 300 ms later by a screen containing a target and two distractor characters. The abrupt-onset precue and the other precue each could be valid or invalid in indicating the location of the target, as in the study by Juola, Koshino, and Warner (1995). Response times to the targets showed that validity effects of the abrupt-onset precue and the MEP or central precue were additive, whereas those of the abrupt-onset precue and the SEP were interactive. These data suggest that, like a central precue, an MEP is an endogenous precue that guides conscious control of attention and has its attentional effects at a different processing level from an SEP, which is an exogenous precue and may compete for attentional resources with an abrupt-onset precue.

Adolescent↗

PubMed1999

Inhibition of return: support for generality of the phenomenon.

Inhibition of return (IOR), first described in 1984, was considered to be a general phenomenon for ensuring that attention would be allocated to successive stimuli in the environment. In the present research, IOR was expressed in forced-choice identification tasks with either reaction time or accuracy as the dependent measure. Thus, the generality of IOR was supported, because response inhibition cannot explain IOR found with accuracy measures. Concepts from the variable and permeable filters metaphor are used to suggest how changes in attention can change expression of IOR by rapid variation in perceptual threshold.

Adolescent↗

PubMed1999

Time course of attention effects with abrupt-onset and offset single- and multiple-element precues.

Large differences between the time course of attentional responsiveness to onset single-element precues (onset singles) and to onset multiple-element precues (onset multiples) have suggested differences in the way attention is controlled. In five experiments here, singles presented as offsets produced rapid attention buildup, attentional decay across longer precue-to-target delays, and attentional capture, as do onset singles, suggesting exogenous attentional control; both offset and onset multiples produced gradual onset of attentional effects without subsequent attentional decay, suggesting endogenous attentional control; and onset and offset singles produced higher accuracy than onset and offset multiples. Thus, the dynamic quality of a sudden onset is not sufficient explanation for the exogenous attentional control produced by a single-element peripheral precue.

Adult↗

PubMed1998

Attention effects of moving and stationary single-element and multiple-element precues: limits of automaticity.

A multiple-element precue (MEP), in which one unique element defines the actual precue, results in efficient precuing for identification of a target. The time course for identification in this case is similar to that for a central precue, even though it is presented peripherally (Chastain, 1996; Chastain & Cheal, in press). Five experiments were conducted to gain further information on the function of MEPs and to question what advantage prior knowledge of the precue may give. In Experiments 1 and 2, it was shown that for "pop-out" features, accuracy of identification of a target was higher if the precue type was known in advance. In contrast, as shown in Experiments 3, 4, and 5, when the precue was defined by apparent motion, there was no difference in accuracy due to advanced knowledge of the precue. Further, accuracy was considerably better for motion precues than for stationary precues.

Attention↗

PubMed1998

Parafoveal identification asymmetry: interactive effects of shape and color.

If two adjacent letters project to the parafoveal region of the retina, both accuracy and discriminability measures have revealed that a letter flanked to its foveal side is identified more accurately than a letter the same distance from the fovea that is flanked to its peripheral side. This parafoveal identification asymmetry is greater if the letters are dissimilar in shape than if they are similar. Color and brightness were introduced as variables in the present experiments. The identification asymmetry was greatest for dissimilar letters in different (complementary) colors. Although those colors differed also in brightness, two letters that were achromatic but merely different in brightness did not produce an asymmetry interaction with shape. Interletter separation was varied between .15 and 1.95 deg, and the pattern of results just described persisted across both distances. The synergistic interaction of shape relation and color relation in determining the amount of identification asymmetry suggests that color and shape affect perceptual processing at the same level.

Adult↗

PubMed1997

Facilitatory or Inhibitory Nontarget Effects in the Location-Cuing Paradigm

The effect of nontargets on the identification of targets in the location-cuing paradigm was investigated in order to determine whether observers consistently allocate their attention to a validly cued location and whether the effect of nontargets is to facilitate or to inhibit performance. In four experiments, the effects of a single matching nontarget or a single nonmatching nontarget were compared. In each experiment, it was shown that observers consistently allocate their attention to a cued location when a precue appears and that performance is inhibited more by nonmatching nontargets in the display than it is facilitated by matching nontargets.

Journal Article↗

PubMed1996

Multiple-element line segment precues: orientation and location effects on attention.

Three experiments were conducted to examine the hypothesis that a uniquely oriented line segment located at the end of the directional flow produced by the alignment of the long axes of identically oriented background segments will not be detected as rapidly as when the segment appears at locations within the flow. The hypothesis was supported with response time measured in Experiment 1. A location-cuing task was used in the last two experiments, with the unique segment becoming a precue to indicate the location of an upcoming target character, accuracy was the dependent measure. Poorer detection of the unique segment at end-of-flow locations was shown not to be due to a local configuration effect produced by the uniquely oriented segment in conjunction with the segment on either side. The time course of attentional development with multiple-segment precue displays was comparable to that with an arrow at fixation as the precue, and slower than that with a line segment appearing alone.

Attention↗

PubMed1996

Attention and nontarget effects in the location-cuing paradigm.

Three experiments were conducted in order to determine whether irrelevant items presented outside the focus of attention would affect the identification of a precued target. A peripheral cue indicated one of eight possible locations in a circular array, centered on fixation with a radius of 5.25 degrees. After a variable interval (0-200 msec), eight characters were presented briefly and masked. In each experiment, there was an effect of the identity of the characters at the seven noncued locations (the nontargets) on the accuracy of identification of the target. When there were more nontargets identical to the target, accuracy was higher than when there were fewer nontargets identical to the target. Nontargets consistently affected performance despite incentives to focus only on the target.

Adult↗

PubMed1992

Analog versus discrete shifts of attention across the visual field.

Two discrimination experiments were run to investigate analog versus discrete properties of a shift of visual spatial attention. Central cuing was used in Experiment 1, whereas peripheral cuing was used in Experiment 2. Presentation of a probe stimulus between fixation and the target (Distance 1), opposite fixation from the target (Distance 3), or away from an imaginary line running from the target through fixation (Distance 2) permitted a fine-grained analysis of attention at those loci across target-probe delays. D-prime analyses in both experiments suggest that attention is shifted in a discrete manner between locations. Sensitivity to probes was generally greater when the probe was aligned with the target and fixation, with Distance 3 equal to Distance 1, than when it was away (at Distance 2). Analysis of sensitivity to targets across cue-probe delays suggests that attention was directed to the probe upon its appearance.

Adult↗

PubMed1992

Is rapid performance improvement across short precue-target delays due to masking from peripheral precues?

The role of lateral masking in more rapid performance improvement with peripheral than with central precuing was investigated. A peripheral precue to the inside of the target location provided less masking at zero precue-target delay than a precue to the outside (experiment 1) or a precue involving a partial target at the target location (experiment 2). There was no significant interaction between precue-target delay and precue type in a comparison of inside precues and precues involving a briefly-brightened box around the target location, although overall performance was significantly poorer with the latter (experiment 3). Performance was better at short precue-target delays with inside precues than with central precues (experiment 4), yet it did not improve significantly more rapidly. Minimizing lateral masking with peripheral precues thus eliminates the dramatic performance improvement sometimes observed across short precue-target delays, causing performance to be consistently better than with central precues across these delays.

Adult↗

PubMed1992

Time-course of sensitivity changes as attention shifts to an unpredictable location.

Shifting visual attention is often described as analogous to a spotlight moving through empty space between locations. In the present experiment, a peripheral precue summoned attention to an initial location, and 200 ms later a second peripheral cue appeared beside one of two possible second locations, each 14 degrees away from the initial location. The target was twice as likely to appear at the location that had been indicated by the immediately preceding cue as at the location that had been previously cued or that would be cued. Fine-grained temporal analyses indicated that, as attention was shifted, sensitivity to information at the second location gradually increased while sensitivity at the first location simultaneously decreased. Average sensitivity over the two locations during the shift remained significantly greater than average sensitivity immediately following the initial precue. In contrast, an attentional "spotlight" moving from the first to the second location would produce a decrease in average sensitivity to its initial level while the spotlight was between locations.

Attention↗

PubMed1991

Effects of abruptly appearing clutter on a peripherally precued covert attention shift.

The effects of clutter that appears abruptly with the target during covert shifts of attention to a precued target location in the visual field were studied. The delay between the appearance of the precue and that of the target with clutter was varied within each block. Blocked conditions included clutter density, the similarity between the shape of the clutter character and that of the target, and whether a clutter character appeared in each path between fixation and the target. Also, a no-clutter control condition was run in this totally within-subject design. Implications of the results for early versus late-selection models of attention were assessed.

Adult↗

PubMed1990

Representation of letters when mislocation errors occur.

Errors in reporting a cued target letter appearing among a string of letters more often reflect the mislocation of a letter appearing elsewhere in the string than the intrusion of one not in the string. The current experiment was conducted to determine the representation of letters at the stage at which errors occur. Four letters (from a set of 12 chosen to contain counterpart pairs that were similar physically, phonemically, or both physically and phonemically) appeared in each exposure, with the target letter indicated by a cue in the postexposure mask. Letter strings presented to one group of subjects were flanked on either side by a pound sign (#) to assess the effect of lateral masking on the terminal letter in the string. Physical similarity dictated the pattern of mislocations between counterparts, suggesting a physical rather than phonemic or abstract representation. Lateral masking played no significant role in the difference between intrusions and mislocations.

Attention↗

PubMed1990

A test of perceptual enhancement with peripherally presented letter pairs.

The present study was conducted to determine whether sensitivity to a member of a pair of stimulus letters projecting to the parafovae would be improved by presenting that member at fixation. The effect was examined for the pair member appearing at a constant distance from fixation, which always was flanked to its inner or outer side. Contrary to expectations based upon results reported by Geiger and Lettvin (1986), observed accuracy changes were found to be due to response bias rather than to sensitivity enhancement.

Attention↗

PubMed1989

Effects of relative position and shape relation on gap detection with geometric form pairs.

A letter presented parafoveally is better identified when flanked by a letter to its foveal side than when flanked by a letter to its peripheral side if the letters are different in shape. If the letters are similar, relative position does not affect identifiability. Whereas some articles in the literature suggest that this effect may not extend to geometric forms, results of the first experiment showed that it does. Results of the second experiment revealed that the strength of the significant interaction between relative position and shape relation remains constant over a range of eccentricities (2-20 deg were tested) extending above and below as well as to the left and right of fixation. Results are compared with predictions from a model that can account for the relative position-shape relation interaction.

Adult↗

PubMed1989

When shape information from a foveal nontarget affects gap detection accuracy in a parafoveal target.

Effects on gap detection accuracy of information at fixation concerning a parafoveally presented target form's global shape were determined in three experiments. Shape information was not directly relevant to the correct response regarding the presence of the gap. Tests were conducted to determine whether costs and benefits were associated with shape information, whether the effectiveness of shape information was sensitive to spatial attention, and whether subjects could volitionally suppress the nontarget information if it became apparent from preattentive analysis that it would not be helpful. Results were positive in all instances. Conclusions were that the foveal information was subject to early selection and that therefore it was not processed automatically.

Attention↗

PubMed1988

Does order of letter analysis contribute to the parafoveal identification asymmetry?

A parafoveally presented target character usually is identified more accurately when flanked by a nontarget character to its foveal side than when flanked by one to its peripheral side. An outside-in process of analysis produced by uncertainty about the target's position could contribute to this asymmetry. Current results revealed a greater asymmetry with relative target position blocked than with it mixed over trials, suggesting that target position uncertainty leads to inside-out, rather than outside-in, analysis.

Fixation, Ocular↗