Biomedical subjects

J T Enns

Publications and source records attributed to J T Enns.

At least 19 recordsLinked to original sources

PubMed2001

Attentional requirements is visual detection and identification: evidence from the attentional blink.

Perception of the 2nd of 2 targets (T1 and T2) is impaired if the lag between them is short (0-500 ms). The authors used this attentional blink (AB) to index attentional requirements in detection and identification tasks, with or without backward masking of T2, in 2 stimulus domains (line orientation, coherent motion). With masking, the AB occurred because T2 was masked during the attentional dwell time created by T1 processing (Experiments 1, 2, and 3). Without masking, an AB occurred only in identification because during the attentional dwell time, T2 decayed to a level that could support simple detection but not complex identification. However, an AB occurred also in detection if T2 was sufficiently degraded (Experiment 4). The authors drew 2 major conclusions: (a) Attention is required in both identification and detection, and (b) 2 factors contribute to the AB, masking of T2 while attention is focused on T1 and decay of the T2 trace while unattended.

Attention↗

PubMed2001

Visual awareness and the on-line modification of action.

An influential theory of visually guided action proposes that (a) conscious perception of target displacement disrupts on-line action and (b) small target perturbations are inconsequential, provided the participant is unaware of them. This study examined these claims in a study of rapid aiming movements to targets. Novel features included on-line verbal reports of target displacement, and the factorial combination of small versus large displacements occurring near peak saccadic velocity or 100 ms later. Although awareness of target displacement had no effect on movement kinematics, even small target displacements near peak saccadic velocity affected kinematic measures. These results support both a strong view of visual stream separation in the on-line control of action and richer spatial coding by unconscious processes than has previously been acknowledged.

Awareness↗

PubMed2001

The role of attention in temporal integration.

When two visual patterns are presented in rapid succession, their contours may be combined into a single unified percept. This temporal integration is known to be influenced by such low-level visual factors as stimulus intensity, contour proximity, and stimulus duration. In this study we asked whether temporal integration is modulated by an attentional-blink procedure. The results from a localisation task in experiment 1 and a detection task in experiment 2 pointed to two separate effects. First, greater attentional availability increased the accuracy of spatial localisation. Second, it increased the duration over which successive stimuli could be integrated. These results imply that theories of visible persistence and visual masking must account for attentional influences in addition to lower-level effects. They also have practical implications for use of the temporal-integration task in the assessment of group and individual differences.

Afterimage↗

PubMed2001

New objects dominate luminance transients in setting attentional priority.

Both the sudden appearance of an object and sudden changes in existing object features influence priority in visual search. However, direct comparisons of these influences have not been made under controlled conditions. In 5 visual search experiments, new object onsets were compared directly with changes in the luminance of old objects. Factors included the luminance contrast of items against the background, the magnitude of luminance change, and the probability that these changes were associated with the target item. New objects were consistently more effective in guiding search, such that a new item with very low luminance contrast was equivalent to an old item undergoing a large change in luminance. An important exception was an old item changing in contrast and polarity, which was as effective as the appearance of a new object. This indicates that search priority is biased toward object rather than situational changes.

Attention↗

PubMed2000

Competition for consciousness among visual events: the psychophysics of reentrant visual processes.

Advances in neuroscience implicate reentrant signaling as the predominant form of communication between brain areas. This principle was used in a series of masking experiments that defy explanation by feed-forward theories. The masking occurs when a brief display of target plus mask is continued with the mask alone. Two masking processes were found: an early process affected by physical factors such as adapting luminance and a later process affected by attentional factors such as set size. This later process is called masking by object substitution, because it occurs whenever there is a mismatch between the reentrant visual representation and the ongoing lower level activity. Iterative reentrant processing was formalized in a computational model that provides an excellent fit to the data. The model provides a more comprehensive account of all forms of visual masking than do the long-held feed-forward views based on inhibitory contour interactions.

Adult↗

PubMed2000

Competition-induced visual field differences in search.

Do visual field effects point to differences in cortical representation, or do they reflect differences in the way these representations are used by other brain regions? This study explored three attributes of visual search that provide strong evidence in favor of differences in use. Competition refers to the finding that visual field differences in search efficiency are larger in whole- than in half-field displays (both left-right and upper-lower half-fields). Task specialization refers to the finding that some tasks favor one hemisphere whereas other tasks favor the other hemisphere, even though the same stimulus displays are used in both tasks. Anatomical alignment refers to the finding that competition effects are altered if the quadrants of the visual display are not aligned with the cortical quadrants of the observer. We propose that visual field specialization in search is the result of a competition involving limited access to cortical visual representations by the extended neural networks of attention.

Adult↗

PubMed2000

Response latencies to the onset and offset of visual stimuli.

Simple response times (RTs) are known to be slower to the offset of a visual stimulus than to its onset. This is called the onset advantage. In the first of four experiments, we discovered that a spurious onset advantage can be produced by the long persistence of P31 phosphor. In the remaining three experiments, we found that offset RTs were slower only when they were made in a context in which responses to the abrupt onset of some stimuli had to be suppressed. We tested this hypothesis of response suppression in two ways: (1) by mixing regular onset trials with other trials on which a response to an onset had to be suppressed, and (2) by ramping the emergence of "offset" stimuli over time, so that offsets were the only abrupt events in the display. In both cases, we found that the onset advantage depended critically on whether the responses were made in a context of response suppression. We conclude that the onset advantage is mediated not by sensory factors such as visible persistence, but by response programming factors that are strongly affected by contextual events.

Humans↗

PubMed2000

Age differences in visual search for compound patterns: long- versus short-range grouping.

Visual search for compound patterns was examined in observers aged 6, 8, 10, and 22 years. The main question was whether age-related improvement in search rate (response time slope over number of items) was different for patterns defined by short- versus long-range spatial relations. Perceptual access to each type of relation was varied by using elements of same contrast (easy to access) or mixed contrast (hard to access). The results showed large improvements with age in search rate for long-range targets; search rate for short-range targets was fairly constant across age. This pattern held regardless of whether perceptual access to a target was easy or hard, supporting the hypothesis that different processes are involved in perceptual grouping at these two levels. The results also point to important links between ontogenic and microgenic change in perception (H. Werner, 1948, 1957).

Adult↗

PubMed1999

The duration of a brief event in the mind's eye.

A new illusion of perceived duration associated with focused spatial attention is reported. Brief flashes in attended locations were perceived to last longer than the same flashes in unattended locations. That illusion was shown to be completely independent of another illusion concerning the perceived onset of a flash, ruling out the possibility that the effect on perceived duration is derivative of a comparison between perceived onset and offset. The illusion also occurred when the event duration was composed of a temporal gap rather than a brief flash, ruling out low-level visible persistence as a basis for the illusion. Taken together, the results point to cortical connections from higher brain centers' both speeding and prolonging the visual signals occurring in lower sensory regions. Those temporal consequences could easily subserve many of the perceptual benefits ascribed to attention for spatial and intensive properties.

Attention↗

PubMed1999

Visual masking plays two roles in the attentional blink.

When two targets are displayed in rapid visual sequence and masked by trailing patterns, identification accuracy is nearly perfect for the first target but follows a U-shaped pattern over temporal lag for the second target. Three experiments examined the role of visual masking in this attentional blink. Experiment 1 compared integration and interruption masks for both targets. Although either mask was effective in producing the blink when applied to the first target, only the interruption mask was effective when applied to the second target. Experiment 2 showed that integration masking of the second target was ineffective over a wide range of accuracy levels. Combining the two forms of masking in Experiment 3 confirmed the dissociation: A combined mask and only a main effect on accuracy for the first target, whereas it produced a qualitatively different pattern over temporal lag for the second target. These results suggest that representations of the target are substituted in consciousness by that of the interruption mask when visual attention is preoccupied.

Adolescent↗

PubMed1998

Early completion of occluded objects.

We show that early vision can use monocular cues to rapidly complete partially-occluded objects. Visual search for easily-detected fragments becomes difficult when the completed shape is similar to others in the display; conversely, search for fragments that are difficult to detect becomes easy when the completed shape is distinctive. Results indicate that completion occurs via the occlusion-triggered removal of occlusion edges and linking of associated regions. We fail to find evidence for a visible filling-in of contours or surfaces, but do find evidence for a 'functional' filling-in that prevents the constituent fragments from being rapidly accessed. As such, it is only the completed structures--and not the fragments themselves--that serve as the basis for rapid recognition.

Adult↗

PubMed1997

Shape completion time depends on the size of the occluded region.

Observers made speeded discriminations of whole, occluded, and mosaic shapes. Shape matching times increased with the amount of occluded shape (Experiment 1), as did the time to merely discriminate 2 shapes (Experiments 2-4). By contrast, the time to judge the shape of the visible portion decreased with larger occluded regions (Experiments 5-7). Experiments 3 and 6 used motion parallax to show that different perceptual operations are involved in discriminating occluded versus mosaic shapes. Experiments 4 and 7 showed that shape completion was unaffected by spatial attention. Results suggest that shape completion is a rapid and obligatory aspect of perception. However, they also show that the time course of completion varies with the size of the hidden region.

Female↗

PubMed1997

Covert visual orienting across the lifespan.

Covert visual orienting was examined over a span of human life ranging from six to 73 years. The observer's task was the speeded discrimination of "X" from "O1" but of primary interest was the effect of a location cue that appeared prior to the target. Both an abrupt stimulus cue and a voluntary information cue were studied using response time (RT) measures. Eye movements were monitored to control for differences in the ability to maintain fixation. Experiment 1 showed that there were very few age differences in stimulus-cued orienting. In contrast, there were important differences when orienting was intentional. In comparison with young adults, children were less able to sustain orienting over time, and senior adults required more time to use the cue. Experiment 2 tested the relation between stimulus and information cues when they both occurred prior to a given target. All age groups were able to use information cues in the presence of conflicting stimulus cues, but young adults were better able to do so than either children or senior adults. These results are interpreted as support for the view that separate mechanisms underlie stimulus-based versus information-based spatial orienting.

Adolescent↗

PubMed1997

Separate influences of orientation and lighting in the inverted-face effect.

Studies of the inverted-face effect typically use photos as stimuli. Inverting photos not only misorients the face but also reverses important shading and shadow cues. We decoupled the influence of spatial orientation and the direction of lighting in three experiments and found that the relation between these factors varied with the task given to observers. When the task required identification of faces (Experiments 1 and 3), the factors were additive, consistent with a strategy of mental rotation of the face prior to an interpretation of the shading cues. When faces were assigned to coarse categories (Experiments 2 and 3), these factors interacted, consistent with a more piecemeal approach to face processing. We propose that the identification of a specific individual depends on configurational information, which is preserved if the image of an inverted face is mentally rotated before the identification process is begun.

Adult↗

PubMed1996

Visual search for size is influenced by a background texture gradient.

Research on the perception of texture gradients has relied heavily on the subjective reports of observers engaged in free-viewing. We asked whether these findings generalized to speeded performance. Experiment 1 showed that an important aspect of subjective perception--size-constancy scaling with perceived distance--also predicted the speed of pop-out visual search for cylinders viewed against a texture gradient. Experiment 2 showed that this finding could not be attributed to the local contrast between search items and the background texture. Experiment 3 assessed the relative contributions of 2 separable dimensions of texture gradients--perspective (radial spreading) and compression (foreshortening)--finding them to be independent in the more rapid search conditions (long target shorter distractors) but combined in the influence in the slower conditions (short target longer distractors).

Adolescent↗

PubMed1996

Pictorial depth and framing have independent effects on the horizontal-vertical illusion.

The method of constant stimuli was used to study the relative contributions of two factors (frame aspect ratio and pictorial depth) on the horizontal-vertical illusion. Four different contexts were created by combining vertically versus horizontally oriented frames with horizontally versus vertically slanted texture gradients. Points of subjective equality and just-noticeable differences were estimated from the psychophysical functions for each observer. The data revealed illusions ranging in size from 10.2% to 4.0% for the various frame-slant combinations, with no associated changes in response variability. The most important finding was that the effects of frame and depth were additive, suggesting that the illusion is determined by at least two different sets of mechanisms.

Cues↗

PubMed1995

Preemption effects in visual search: evidence for low-level grouping.

Experiments are presented showing that visual search for Mueller-Lyer stimuli is based on complete configurations rather than component segments. Segments easily detected in isolation were difficult to detect when embedded in a configuration, indicating preemption by low-level groups. This preemption--which caused stimulus components to become inaccessible to rapid search--was an all-or-nothing effect and so could serve as a powerful test of grouping. It is shown that these effects are unlikely to be due to blurring by simple spatial filters at early visual levels. It is proposed instead that they are due to more sophisticated processes that rapidly blind contour fragments into spatially extended assemblies. These results support the view that rapid visual search cannot access the primitive elements formed at the earliest stages of visual processing; rather, it can access only higher level, more ecologically relevant structures.

Attention↗

PubMed1995

Search for letter identity and location by disabled readers.

Reading-disabled boys, reading- and age-matched controls, and adults searched letter arrays for the identity or location of a probe letter. Response time (RT) and accuracy were examined as a function of the temporal relation between probe and array letters (probe first, simultaneous, array first), and array size (1-5 letters). Although disabled readers closely resembled age controls in RT, their accuracy differed significantly when large letter arrays were tested. In the letter identification task, this was only evident when the array letters preceded the probe; in the letter location task, it occurred in all three probe conditions. Correlational analyses showed that all subjects were influenced by the visual, but not the phonological, similarity between letters. Thus, a reading-related impairment is evident in both letter identification and letter location processes, even when the phonological coding of letters has been minimized.

Adolescent↗