Biomedical subjects

James T Enns

Publications and source records attributed to James T Enns.

29 records · Page 2Linked to original sources

PubMed2004

Decoupling stimulus duration from brightness in metacontrast masking: data and models.

A brief target that is visible when displayed alone can be rendered invisible by a trailing stimulus (metacontrast masking). It has been difficult to determine the temporal dynamics of masking to date because increments in stimulus duration have been invariably confounded with apparent brightness (Bloch's law). In the research reported here, stimulus luminance was adjusted to maintain constant brightness across all durations. Increasing target duration yielded classical U-shaped masking functions, whereas increasing mask duration yielded monotonic decreasing functions. These results are compared with predictions from 6 theoretical models, with the lateral inhibition model providing the best overall fit. It is tentatively suggested that different underlying mechanisms may mediate the U-shaped and monotonic functions obtained with increasing durations of target and mask, respectively.

Cerebral Cortex↗

PubMed2004

Negative compatibility or object updating? A cautionary tale of mask-dependent priming.

The negative compatibility effect (NCE) is the surprising result that visual targets that follow a brief prime stimulus and a mask can be identified more rapidly when they are opposite rather than identical to the prime. In a recent article in this journal, S. T. Klapp and L. B. Hinkley (2002) proposed that this reflected a competition between inhibitory unconscious processes and excitatory conscious processes. The authors of the current article report 7 experiments with results countering this theory and propose an alternative account within the framework of object substitution masking. In this account, the NCE reflects the updating of perceptual objects, including their links to responses closely associated with those objects.

Discrimination, Psychological↗

PubMed2004

Object updating and the flash-lag effect.

Flash lag is a misperception of spatial relations between a moving object and a briefly flashed stationary one. This study began with the observation that the illusion occurs when the moving object continues following the flash, but is eliminated if the object's motion path ends with the flash. The data show that disrupting the continuity of the moving object, via a transient change in size or color, also eliminates the illusion. We propose that this is because a large feature change leads to the formation of a second object representation. Direct evidence for this proposal is provided by the results for a corollary perceptual feature of the disruption in object continuity: the perception of two objects, rather than only one, on the motion path.

Analysis of Variance↗

PubMed2004

Influence of inter-item symmetry in visual search.

Does visual search involve a serial inspection of individual items (Feature Integration Theory) or are items grouped and segregated prior to their consideration as a possible target (Attentional Engagement Theory)? For search items defined by motion and shape there is strong support for prior grouping (Kingstone and Bischof, 1999). The present study tested for grouping based on inter-item shape symmetry. Results showed that target-distractor symmetry strongly influenced search whereas distractor-distractor symmetry influenced search more weakly. This indicates that static shapes are evaluated for similarity to one another prior to their explicit identification as 'target' or 'distractor'. Possible reasons for the unequal contributions of target-distractor and distractor-distractor relations are discussed.

Adult↗

PubMed2004

Mislocalizations of touch to a fake hand.

Observers can mislocalize a tactile target delivered to an unseen hand if a visible rubber glove is positioned next to a pair of distractor lights that flash in correlation with the tactile target (Pavani, Spence, & Driver, 2000). In the present study, we explored visual, tactile, and postural factors that influence this fake hand effect. Comparison with baseline conditions revealed that the fake hand effect was larger than a general spatial congruity effect but weaker than the effect obtained when tactile and visual stimuli were actually in the same locations (Experiment 1). Surprisingly, the effect did not depend on direct vision of the fake hand (Experiments 1 and 2), nor was it enhanced by congruent tactile information (Experiment 3). However, the fake hand effect was sensitive to the postural compatibility of the real and the fake hands (Experiment 4). These findings indicate that the available sensory information is used flexibly to incorporate the rubber glove into the body schema.

Artificial Limbs↗

PubMed2003

Locally oriented perception with intact global processing among adolescents with high-functioning autism: evidence from multiple paradigms.

BACKGROUND: According to predictions from the Weak Central Coherence (WCC) theory for perceptual processing, persons with autism should display a tendency to focus on minute details rather than on a more general picture (Frith & Happé, 1994). However, the evidence for this theory is not consistent with findings of an enhanced detection of local targets (Plaisted, O'Riordan, & Baron-Cohen, 1998b; Plaisted, Swettenham, & Rees, 1999), but a typical global bias (Mottron, Burack, Stauder, & Robaey, 1999; Ozonoff, Strayer, McMahon, & Filloux, 1994). METHOD: Adolescents with high-functioning autism and CA- (approximately 15 years) and IQ- (approximately 105-110) matched typically developing adolescents were administered a series of global-local visual tasks, including a traditional task of hierarchical processing, three tasks of configural processing, and a disembedding task that involved rapid perceptual processing. RESULTS: No group differences were found on either the traditional task of hierarchical processing or on tasks of configural processing. However, group differences were found on the disembedding task as the search for embedded, in relation to isolated stimuli, was slower for the typically developing adolescents but similar for the participants with autism. CONCLUSIONS: These findings are consistent with other reports of superior performance in detecting embedded figures (Jolliffe & Baron-Cohen, 1997; Shah & Frith, 1983), but typical performance in global and configural processing (Mottron, Burack et al., 1999; Ozonoff et al., 1994) among persons with high-functioning autism. Thus, the notions of local bias and global impairment that are part of WCC may need to be reexamined.

Adolescent↗

PubMed2003

Change detection in an attended face depends on the expectation of the observer.

Sensitivity to a scene change during a brief interruption depends critically on a match between what the observer expects to see and the kind of change that occurs (Austen & Enns, 2000). The present study tested the generality of this conclusion using human faces, which are both socially more relevant and perceptually more configural than the compound letters tested previously. An experiment using the flicker technique examined sensitivity to two types of change: facial identity and emotional expression. Change detection was assessed when attention was either focused or distributed, the change was either expected or unexpected, and the faces were either upright or inverted. The main finding was that detection was expectation-dependent, even when only a single upright face was presented. Secondary findings with regard to attentional distribution and face inversion confirmed that observers were indeed engaged in face processing. We conclude that observer expectations critically influence the perception of single and fully attended human faces.

Attention↗

PubMed2003

Task switching mediates the attentional blink even without backward masking.

When two targets are presented in rapid succession, perception of the second target is impaired at short intertarget lags (100-700 msec). This attentional blink (AB) is thought to occur only when the second target is backward masked. To the contrary, we show that task switching between the targets can produce an AB even without masking (Experiments 1 and 3). Further, we show that task switching produces an AB only when the second target does not belong to a class of overlearned stimuli such as letters or digits (Experiments 1 and 4). When the second target is masked, however, an AB is invariably obtained regardless of switching or overlearning. We propose that task switching involves a time-consuming process of reconfiguration of the visual system, during which the representation of the second target decays beyond recognition, resulting in an AB deficit. We suggest that overlearned stimuli are encoded in a form that, while maskable, decays relatively slowly, thus outlasting the delay due to reconfiguration and avoiding the AB deficit.

Attention↗

PubMed2003

Target detection and localization in visual search: a dual systems perspective.

The dual visual systems framework (Milner & Goodale, 1995) was used to explore target detection and localization in visual search. Observers searched for a small patch of tilted bars against a dense background of upright bars. Target detection was performed along with two different localization tasks: direct pointing, designed to engage the dorsal stream, and indirect pointing, designed to engage the ventral stream. The results indicated that (1) target detection was influenced more by orientation differences in 3-D space than by 2-D pictorial differences, (2) target localization was more accurate for direct than for indirect pointing, and (3) there were performance costs for indirect localization when it followed target detection, but not for direct localization. This is consistent with direct localization's having greater dependence on the dorsal visual system than either target detection or indirect localization.

Adult↗

PubMed2002

Visual orienting in college athletes: explorations of athlete type and gender.

Covert orienting was measured in 50 college athletes and 51 nonathletes of both genders. Visual environments of the sports were both static (swimming, track) and dynamic (soccer, volleyball). Participants made speeded responses in a task measuring vigilance, alerting, automatic orienting, voluntary orienting, modulation of automatic orienting, and modulation of inhibition of return. Gender differences werefound in the overall response times of nonathletes and in the alerting measures for all participants. However, all participants were similar in their automatic orienting. Sport-specific effects were seen in voluntary orienting and in the modulation of automatic orienting. These gender and sports-related findings are interpreted in light of the experience athletes have in the dynamic control of spatial attention.

Adult↗

PubMed2002

Visual binding in the standing wave illusion.

When two video frames are alternated at the appropriate rate, one with a central bar and the other with two flanking bars, the central bar becomes invisible. Competing explanations for this standing wave illusion are examined, with the results showing an influence of higher level shape representations on lower level edge processes. In Experiment 1, flanking bar duration was found to be more important to masking than central bar duration. Experiment 2 showed strong nonlocal effects in that masking of the central bar depended critically on whether it appeared in the same video frame as other visible bars. Experiments 3 and 4 showed that the contour shared by bars in separate frames was a less important factor than shape and surface similarity. This illusion is therefore an excellent tool for studying recursive interactions between higher level object representations and lower level contour processes.

Humans↗