Biomedical subjects

James T Enns

Publications and source records attributed to James T Enns.

At least 19 recordsLinked to original sources

PubMed2006

On-line control of pointing is modified by unseen visual shapes.

Shapes that are rendered invisible through backward masking are still able to influence motor responses: this is called masked priming. Yet it is unknown whether this influence is on the control of ongoing action, or whether it merely influences the initiation of an already-programmed action. We modified a masked priming procedure (Schmidt, 2002) such that the critical prime-mask sequence was displayed during the execution of an already-initiated goal-directed pointing movement. Psychophysical tests of prime visibility indicated that the identity of the prime shapes were not accessible to participants for conscious report. Yet detailed kinematic analysis of the finger in motion revealed that masked primes had an influence on the pointing trajectories within 277ms of their appearance, 56ms earlier than the trajectory deviations observed in response to the visible masks. These results indicate that subliminal shapes can indeed influence the control of ongoing motor activity.

Adult↗

PubMed2006

Global-local visual processing in high functioning children with autism: structural vs. implicit task biases.

Global-local processing was examined in high-functioning children with autism and in groups of typically developing children. In experiment 1, the effects of structural bias were tested by comparing visual search that favored access to either local or global targets. The children with autism were not unusually sensitive to either level of visual structure. In experiment 2 a structural global bias was pitted against an implicit task bias favoring the local level. Children with autism were least sensitive to the structural global bias but showed greater sensitivity to the implicit task bias. This suggests that autism is associated with differences in the executive control processes used to guide attention to either the global or local level, and strategies may be more "data driven".

Attention↗

PubMed2006

How much like a target can a mask be? Geometric, spatial, and temporal similarity in priming: a reply to Schlaghecken and Eimer (2006).

The authors make 3 points in response to F. Schlaghecken and M. Eimer's proposal of self-inhibition as an explanatory factor in the negative compatibility effect: (a) The self-inhibition hypothesis lacks empirical support for its main tenets; (b) considering the roles of geometric, spatial, and temporal similarity of primes and masks makes self-inhibition unnecessary; and (c) the negative compatibility effect occurs even when the main tenets of self-inhibition are violated. The authors propose that understanding what is "relevant" in a masked-priming task applies not only to geometric features that are shared with the target but to spatial and temporal ones as well. Briefly, target-mask similarity determines how motor preparation is accumulated during the prime-mask sequence.

Adult↗

PubMed2006

The development of change detection.

Changes to a scene often go unnoticed if the objects of the change are unattended, making change detection an index of where attention is focused during scene perception. We measured change detection in school-age children and young adults by repeatedly alternating two versions of an image. To provide an age-fair assessment we used a bimanual choice rather than open-ended verbal responses. The difference in detection speed and accuracy between 50-ms versus 250-ms blank screens between views indexed change detection in short-term visual memory independent of sensory and response processes. Younger children were significantly less efficient than older participants, especially when an object changed color or had a part deleted. Changes in object orientation were detected more readily. These results point to important differences in the perceptual reality of younger and older children.

Adolescent↗

PubMed2006

New reflections on visual search: Interitem symmetry matters!

A 90 degrees rotation of a display can turn a relatively easy visual search into a more difficult one. A series of experiments examined the possible causes of this effect, including differences in overall item shape and response mapping (Experiment 1), the interpretation of scene lighting (Experiment 2), the axis of internal symmetry of the search items (Experiment 3), and the axes of interitem symmetry between target and distractor items (Experiment 4). Only the elimination of differences in interitem mirror symmetry resulted in equal search efficiency in the upright and rotated displays. This finding is strong support for the view that visual search is guided by an analysis that considers interitem relations.

Form Perception↗

PubMed2006

Observer pitch and roll influence: the rod and frame illusion.

Observers misperceive the orientation of a vertical rod when it is viewed in the context of a tilted frame (the rod and frame illusion, or RFI). The pitch and roll of the surrounding surfaces have independent influences on this illusion (Nelson and Prinzmetal, 2003). Experiment 1 measured the RFI when the pitch and roll of the floor that supported the observer was varied, and the observer was either seated in a chair or standing upright. There were additive influences of pitch and roll on the RFI of seated but not standing observers. Experiments 2 and 3 decoupled body roll and head roll in order to isolate the vestibular and proprioceptive contributions to these effects. The results are interpreted in support of a hierarchy of influence on the RFI: Visual input is given top priority, followed by vestibular input, and then proprioceptive input.

Adolescent↗

PubMed2005

The attentional blink is not a unitary phenomenon.

Identification of the second of two targets is impaired if it is presented less than about 500 ms after the first. Three models of this second-target deficit, known as attentional blink (AB), were compared: resource-depletion, bottleneck, and temporary loss of control (TLC). Five experiments, in which three sequential targets were inserted in a stream of distractors, showed that identification accuracy for the leading target depended on an attentional switch whose magnitude varied with distractor-target similarity. In contrast, accuracy for the trailing target depended on similarity between the target and the trailing mask. These results strongly suggest that the AB is not a unitary phenomenon. Resource-depletion was ruled out as a viable account. The effect of attentional switching was handled naturally by the TLC model, while bottleneck models offered the best account of the effect of backward masking.

Attention↗

PubMed2005

No automatic pilot for visually guided aiming based on colour.

It has been claimed that visually guided limb movements are automatically corrected in response to a change in target location but not when the same change in target is cued through a colour switch (Pisella et al. 2000). These findings were based solely on limb endpoint data. Here we examine the kinematic trajectory of the hand during the entire movement. Participants pointed rapidly to a target object that could change position either by changing spatial location, or by switching colour with a second object. Participants performed in two instructional conditions: a "go" condition to index intentional movements and a "stop" condition in which failures to stop pointing indexed automatic limb guidance. Kinematic analysis indicated efficient intentional pointing in both location and colour change conditions. However, only targets that changed spatial location elicited involuntary limb modifications and these occurred within 150 ms of the change. This conclusion held even after baseline differences in the efficiency of processing colour-defined targets were taken into account, thereby strengthening the claim of a strongly automatic pilot for visually guided limb movements.

Adolescent↗

PubMed2005

Visual letter matching: hemispheric functioning or scanning biases?

Finding two mixed-case letters that share the same name is easier to do when the letters are presented in opposite visual fields than when they are both in the same field. By contrast, finding a match between two same-case letters is easier when they are in the same field. These visual field effects have been attributed to the ability of the corpus callosum to coordinate the work of the cerebral hemispheres [Banich, M. T. (1998). The missing link: The role of interhemispheric interaction in attentional processing. Brain and Cognition, 36, 128-157; Weissman, D. H., & Banich, M. T. (2000). The cerebral hemispheres cooperate to perform complex but not simple tasks. Neuropsychology, 14, 41-59]. The present study considers the alternative hypothesis that attentional scanning biases may be at work. Experiment 1 examined the effects of explicit instructions to scan items in a specific order; Experiment 2 examined influences of implicit location biasing; Experiment 3 considered the possibility that same-case letter matching is different because a perceptual grouping mechanism can be used in that task. In each experiment, we first interpreted the results within the hemispheric framework before considering the alternative accounts. We concluded that two scanning biases may be in effect: (1) an automatic bias favoring items in locations relatively distant from the current focus of attention and (2) a learned bias to scan letters in a left-to-right direction.

Analysis of Variance↗

PubMed2005

Multiple-object tracking is based on scene, not retinal, coordinates.

This study tested whether multiple-object tracking-the ability to visually index objects on the basis of their spatiotemporal history-is scene based or image based. Initial experiments showed equivalent tracking accuracy for objects in 2-D and 3-D motion. Subsequent experiments manipulated the speeds of objects independent of the speed of the scene as a whole. Results showed that tracking accuracy was influenced by object speed but not by scene speed. This held true whether the scene underwent translation, zoom, rotation, or even combinations of all 3 motions. A final series of experiments interfered with observers' ability to see a coherent scene by moving objects at different speeds from one another and by distorting the perception of 3-D space. These reductions in scene coherence led to reduced tracking accuracy, confirming that tracking is accomplished using a scene-based, or allocentric, frame of reference.

Adult↗

PubMed2005

Rapid resumption of interrupted visual search. New insights on the interaction between vision and memory.

A modified visual search task demonstrates that humans are very good at resuming a search after it has been momentarily interrupted. This is shown by exceptionally rapid response time to a display that reappears after a brief interruption, even when an entirely different visual display is seen during the interruption and two different visual searches are performed simultaneously. This rapid resumption depends on the stability of the visual scene and is not due to display or response anticipations. These results are consistent with the existence of an iterative hypothesis-testing mechanism that compares information stored in short-term memory (the perceptual hypothesis) with information about the display (the sensory pattern). In this view, rapid resumption occurs because a hypothesis based on a previous glance of the scene can be tested very rapidly in a subsequent glance, given that the initial hypothesis-generation step has already been performed.

Humans↗

PubMed2005

Unique temporal change is the key to attentional capture.

Attentional capture refers to the observation that some events break through and attract one's attention even when one is engaged in a task for which these events are irrelevant. Previous research, focusing primarily on spatial factors, has shown that a new object is more salient in this regard than an abrupt change in an object's features. Here we show that feature changes can be as effective as new objects in capturing attention, provided that they occur during a period of temporal calm. Conversely, both feature changes and new objects are far less effective in capturing attention when they occur simultaneously with other display changes, such as coincident with the initial onset of the display or with small visual transients that occur during a display transition. These results highlight the importance of considering both space and time in studies of attentional capture; the most effective stimulus is unique in both dimensions.

Adolescent↗

PubMed2005

Voluntary orienting among children and adolescents with Down syndrome and MA-matched typically developing children.

A forced-choice reaction-time (RT) task was used to examine voluntary visual orienting among children and adolescents with trisomy 21 Down syndrome and typically developing children matched at an MA of approximately 5.6 years, an age when the development of orienting abilities reaches optimal adult-like efficiency. Both groups displayed faster reaction times (RTs) when the target location was cued correctly than when cued incorrectly under both short and long SOA conditions, indicating intact orienting among children with Down syndrome. This finding is further evidence that the efficiency of many of the primary components of attention among persons with Down syndrome is consistent with their developmental level.

Adolescent↗

PubMed2005

The edge complex: implicit memory for figure assignment in shape perception.

Viewing a stepped edge is likely to prompt the perceptual assignment of one side of the edge as figure. This study demonstrates that even a single brief glance at a novel edge gives rise to an implicit memory regarding which side was seen as figure; this edge complex enters into the figure assignment process the next time the edge is encountered, both speeding same-different judgments when the figural side is repeated and slowing these judgments when the new figural side is identical to the former ground side (Experiments 1A and 1B). These results were obtained even when the facing direction of the repeated edge was mirror reversed (Experiment 2). This study shows that implicit measures can reveal the effects of past experience on figure assignment, following a single prior exposure to a novel shape, and supports a competitive model of figure assignment in which past experience serves as one of many figural cues.

Cues↗

PubMed2004

What the hand can't tell the eye: illusion of space constancy during accurate pointing.

When we press an elevator button or pick up a coffee cup, different visual information is used to guide our reach and to form our conscious experience of these objects. But can the information guiding our hand be brought into awareness? The fact that we can see and feel our own hand in action suggests that it might be possible. However, the dual visual systems theory claims that on-line control of movement is governed by the dorsal stream of visual processing, which is largely unconscious. Two experiments are presented as strong tests of the hypothesis that the visual information guiding on-line pointing in healthy human adults is inaccessible for conscious report. Results show that participants are incapable of consciously accessing the information used in pointing, even though they can see and feel their hands in action and accurate performance depends on it.

Biomechanical Phenomena↗

PubMed2004

The attentional blink: resource depletion or temporary loss of control?

Identification of the second of two targets is impaired if it is presented less than about 500 ms after the first. Theoretical accounts of this second-target deficit, known as attentional blink (AB), have relied on some form of limited attentional resource that is allocated to the leading target at the expense of the trailing target. Three experiments in the present study reveal a failure of resource-limitation accounts to explain why the AB is absent when the targets consist of a stream of three items belonging to the same category (e.g., letters or digits). The AB is reinstated, however, if an item from a different category is inserted in the target string. This result, and all major results in the AB literature, is explained by the hypothesis that the AB arises from a temporary loss of control over the prevailing attentional set. This lapse in control renders the observer vulnerable to an exogenously-triggered switch in attentional set.

Analysis of Variance↗

PubMed2004

Hemisphere differences in conscious and unconscious word reading.

Hemisphere differences in word reading were examined using explicit and implicit processing measures. In an inclusion task, which indexes both conscious (explicit) and unconscious (implicit) word reading processes, participants were briefly presented with a word in either the right or the left visual field and were asked to use this word to complete a three-letter word stem. In an exclusion task, which estimates unconscious word reading, participants completed the word stem with any word other than the prime word. Experiment 1 showed that words presented to either visual field were processed in very similar ways in both tasks, with the exception that words in the right visual field (left hemisphere) were more readily accessible for conscious report. Experiment 2 indicated that unconsciously processed words are shared between the hemispheres, as similar results were obtained when either the same or the opposite visual field received the word stem. Experiment 3 demonstrated that this sharing between hemispheres is cortically mediated by testing a split-brain patient. These results suggest that the left hemisphere advantage for word reading holds only for explicit measures; unconscious word reading is much more balanced between the hemispheres.

Adult↗

PubMed2004

Object substitution and its relation to other forms of visual masking.

Three experiments compared letter identification accuracy over a wide range of target-mask intervals and mask types, including metacontrast, random dot noise, four surrounding dots, digits and letters. These comparisons were motivated by object substitution theory which makes three general predictions about visual masking: (1) very different looking backward masks will be equivalent in their effects when spatial attention is distributed, such that target identification is delayed, (2) masks will differ most in their effects on target identification when they are temporally integrated with the target, and (3) backward masking will be minimized when attention can be pre-focused on the spatial location of the target and the mask does not interfere with target identification. Results strongly supported the predictions and pointed to a new understanding of masking based on the separate processes of object formation and object substitution.

Attention↗