James T. Enns

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.

What's new in visual masking?

A brief display that is clearly visible when shown alone can be rendered invisible by the subsequent presentation of a second visual stimulus. Several recently described backward masking effects are not predicted by current theories of visual masking, including masking by four small dots that surround (but do not touch) a target object and masking by a surrounding object that remains on display after the target object has been turned off. A crucial factor in both of these effects is attention: almost no masking occurs if attention can be rapidly focused on the target, whereas powerful masking ensues if attention directed at the target is delayed. A new theory of visual masking, inspired by developments in neuroscience, can account for these effects, as well as more traditional masking effects. In addition, the new theory sheds light on related research, such as the attentional blink, inattentional blindness and change blindness.

Object Substitution: A New Form of Masking in Unattended Visual Locations

Can four dots that surround, but do not touch, a target shape act as a mask to reduce target discriminability? Although existing theories of metacontrast and pattern masking say “no,” we report this occurs when targets appear in unpredictable locations. In three experiments, a four-dot mask was compared with a standard metacontrast mask that surrounded the target. Although accuracy was predictably different for the two masks at a central display location in Experiment I, both masks had similar strong effects on accuracy in parafoveal locations. Experiment 2 revealed that both four-dot and metacontrast masking were insensitive to contour proximity in parafoveal display locations, and Experiment 3 showed that four-dot masking could occur even at a central location if attention was distributed among several targets. We propose that targets in unattended locations are coded with low spotiotemporal resolution, leaving them vulnerable to substitution by the four dots when attention is directed to them.

Preattentive recovery of three-dimensional orientation from line drawings

It has generally been assumed that rapid visual search is based on simple features and that spatial relations between features are irrelevant for this task. Seven experiments involving search for line drawings contradict this assumption; a major determinant of search is the presence of line junctions. Arrow- and Y-junctions were detected rapidly in isolation and when they were embedded in drawings of rectangular polyhedra. Search for T-junctions was considerably slower. Drawings containing T-junctions often gave rise to very slow search even when distinguishing arrow- or Y-junctions were present. This sensitivity to line relations suggests that preattentive processes can extract 3-dimensional orientation from line drawings. A computational model is outlined for how this may be accomplished in early human vision.

The development of selective attention: a life-span overview.

This paper outlines research on selective attention within a life-span developmental framework. Findings obtained in both the infancy-child and adulthood-aging literatures are reviewed and discussed in relationship to four aspects of selective attention: orienting, filtering, search, and expecting. Developmental consistencies and inconsistencies are identified and integrative theories are evaluated. Although a single theory is unlikely to accommodate the diverse patterns of age effects, emergent themes are identifiable nonetheless and the essential ingredients of a life-span theory of attentional development are enumerated. Directions for future research and theory are suggested.

Large datasets at a glance: combining textures and colors in scientific visualization

We present a new method for using texture and color to visualize multivariate data elements arranged on an underlying height field. We combine simple texture patterns with perceptually uniform colors to increase the number of attribute values we can display simultaneously. Our technique builds multicolored perceptual texture elements (or pexels) to represent each data element. Attribute values encoded in an element are used to vary the appearance of its pexel. Texture and color patterns that form when the pexels are displayed can be used to rapidly and accurately explore the dataset. Our pexels are built by varying three separate texture dimensions: height, density, and regularity. Results from computer graphics, computer vision, and human visual psychophysics have identified these dimensions as important for the formation of perceptual texture patterns. The pexels are colored using a selection technique that controls color distance, linear separation, and color category. Proper use of these criteria guarantees colors that are equally distinguishable from one another. We describe a set of controlled experiments that demonstrate the effectiveness of our texture dimensions and color selection criteria. We then discuss new work that studies how texture and color can be used simultaneously in a single display.

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.

High-speed visual estimation using preattentive processing

A new method is presented for performing rapid and accurate numerical estimation. The method is derived from an area of human cognitive psychology called preattentive processing. Preattentive processing refers to an initial organization of the visual field based on cognitive operations believed to be rapid, automatic, and spatially parallel. Examples of visual features that can be detected in this way include hue, intensity, orientation, size, and motion. We beleive that studies from preattentive vision should be used to assist in the design of visualization tools, especially those for which high-speed target detection, boundary identification, and region detection are important. In our present study, we investigated two known preattentive features (hue and orientation) in the context of a new task (numerical estimation) in order to see whether preattentive estimation was possible. Our experiments tested displays that were designed to visualize data from salmon migration simulations. The results showed that rapid and accurate estimation was indeed possible using either hue or orientation. Furthermore, random variation in one of these features resulted in no interference when subjects estimated the percentage of the other. To test the generality of our results, we varied two important display parameters—display duration and feature difference—and found boundary conditions for each. Implications of our results for application to real-world data and tasks are discussed.

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.

Relations between Covert Orienting and Filtering in the Development of Visual Attention.

This study examined a widely held assumption concerning the development of visual attention, namely, that different aspects of visual selectivity depend on common processing resources. Observers aged 5, 7, 9, and 24 years participated in a speeded classification task designed to examine the relations between covert shifts of attention and filtering. There were three important findings: (1) covert orienting and filtering share processing resources, (2) the ability to orient covertly to a target location and to filter competing information on the same trial became more efficient with age, and (3) 5 year olds were able to filter as efficiently as adults when target location was precued. The implications of these results for theories of attentional development are discussed.