Cognitive Psychology

James E. Hoffman

		Professor Ph.D., University of Illinois, Champaign-Urbana, 1974 Research Interests Recent Publications Representative Publications Web site Vita -MS Word file hoffman@psych.udel.edu Office: 213 Wolf Hall (302) 831-2453 (302) 831-3645 -fax Lab: 414 Wolf Hall (302) 831-1137 Preferred contact method - email Research Opportunities undergraduate

Research Interests

Visual Cognition, Selective Attention, Williams Syndrome, Event-related Brain Potentials

Research Summary:

It may not be obvious but the visual world contains much more information than we can perceive in a “single glance”. For example, experiments on “change blindness” indicate that observes have detailed information about only 3-4 objects following a single fixation on a typical scene. Luckily, we have sophisticated selection mechanisms that help us choose objects of importance based on our current goals and expectations, and we are rarely aware of our limited capacity to process more than a few objects at a time. For example, overt attention mechanisms consist of changes in the orientation of our head, eyes and body to concentrate on regions of interest. They are overt because they are visible to other people and, indeed, we are extremely sensitive to the direction of gaze of those around us as this provides an important social clue about their interest in us. There is also a “covert attention” mechanism whose operation is not visible to others which allows us to pay attention without any changes in the location of gaze. This is accomplished through specialized circuits in various areas of the visual system which act to amplify the signals associated with attended regions of space.

How do these two selection systems work together to guide our behavior? We (Hoffman and Subramaniam, 1995) found that they are closely linked; in particular it appears that eye movements directed to a location in space are preceded by a covert shift of visual attention to that same location. Indeed, it appears that a variety of different kinds of eye movements, including saccades and pursuit and vergence movements are preceded by covert shifts of attention (Hoffman, 1998).

Covert attention experiments usually require observers to pay attention to an empty region of space in anticipation of an object that will appear there. These experiments suggest that spatial attention has a coarse grain and encompasses the attended object as well as nearby objects. This feature of attention places strict limits on our ability to pay attention to one object in a crowded field, a phenomenon known as “crowding”. However, under the right circumstances, we are quire good at disentangling an object from surrounding clutter using a mechanism known as “object-based attention”. We have recently used event-related brain potentials (ERPs) to show that object-based attention can help us select one of two overlapping objects that are both contained with in the coarse-grained spotlight of spatial attention. In other words, these two systems appear to work together with the spatial system using a coarse grained “spotlight” to choose an area of interest in the visual field. Objects of interest within the attended region are then highlighted by the object-based system. Studying how these two attention systems operate and interact is a current research focus of my lab

Williams Syndrome

Together with Barbara Landau, who is in the Cognitive Science Department at Johns Hopkins University, I have been attempting to use what we have learned about spatial cognition in adults to help us understand the nature of spatial deficits in children with Williams Syndrome. Williams Syndrome (WS) is a rare (1 in 20,000 births) genetic disorder that results in a unique phenotypic pattern that includes a characteristic facial profile, disorders of the heart, and anomalies of the viscera. I addition, they display an unusual and distinctive cognitive profile consisting of strong language abilities and severely impaired visuo-spatial skills. This unique pattern of sparing and impairments in the cognitive domain has been taken by some investigators as support for the idea that the human mind consists of separate modules that are responsible for different areas of mental life such as talking, seeing, and thinking.

Our current hypothesis is that spatial deficits associated WS may be due to delayed and arrested development of certain structures in the dorsal stream of the visual system, particularly regions of the parietal cortex that are concerned with a wide variety of visual functions including visually guided action. In contrast, the ventral visual stream, which is concerned with recognition of objects and faces, appears to be largely intact in people with WS, consistent with their ability to identify faces and common objects.

Recent Publications

Doran, M., Hoffman, J. E., & Scholl, B. (in press).The Role of Eye Fixations in Concentration and Amplification Effects During Multiple Object Tracking. Visual Cognition.

Quinn, P. C., Doran, M. M., Reiss, J. E., & Hoffman, J. E. (in press). Time course of visual attention in infant categorization of cats versus dogs: Evidence for a head bias as revealed through eye tracking. Child Development.

Landau, B. L., O’Hearn, K., & Hoffman, J. E. (in press). Tethering to the World, Coming Undone. Chapter in L. B. Smith (Ed.), Volume in Spatial Language Series, Indiana University Press.

Dilks, D. D., Hoffman, J. E., and Landau, B. L. (2008). Vision for perception and vision for action: normal and unusual development. Developmental Science, 11:4, 474 –486

Reiss, J. E. & Hoffman, J. E. (2007). Disruption of Early Face Recognition Processes by Object Substitution Masking. Visual Cognition, 15 (7), 789-798.

Landau, B. L., & Hoffman, J. E. (2007) Explaining selective spatial breakdown in Williams Syndrome: Four principles of normal spatial development and why they matter. In J. Plumert and J. Spencer (Eds.), Emerging landscapes of Mind: Mapping the nature of change in spatial cognitive development. Pages 290-319. Oxford University Press.

Intraub, H., Hoffman, J. E., Wetherhold, C. J., & Stoehs, S. A. (2006). More than meets the eye: The effect of planned fixations on scene representation. Perception & Psychophysics, 68(5), 759-769.

Elzer, S., Green, N., Carberry, S., & Hoffman, J. E. (2006). A Model of Perceptual Task Effort for Bar Charts and its Role in Recognizing Intention. User Modeling and User-Adapted Interaction, 16 (1): 1-30. Winner of the 2006 James Chen Annual Award for Best User Modeling and User-Adapted Interaction Paper.

Reiss, J. E. & Hoffman, J. E. (2006). Object Substitution Masking Interferes With Semantic Processing: Evidence From Event-Related Potentials. Psychological Science, 17, 1015-1020

Landau, B., Hoffman, J.E., & Kurz, N. (2006). Object recognition with severe spatial deficits in Williams syndrome: sparing and breakdown. Cognition, 100 (3): 483-510.

Reiss, J. E., Hoffman, J. E., & Landau, B. (2005). Motion processing specialization in Williams syndrome. Vision Research, 45(27), 3379-3390.

O’Hearn, K., Landau, B., & Hoffman, J. E. Multiple Object Tracking in People with Williams Syndrome and in Normally Developing Children. (2005). Psychological Science, 16(11), 905-912.

Landau, B., Hoffman, J. E., Reiss, J., Dilks, D.D., Lakusta, L., & Chunyo, G. Specialization and Breakdown in Spatial Cognition: Lessons from Williams syndrome. To appear in C. Morris, H. Lenhoff, & P. Wang (Eds.), Williams-Beuren Syndrome: Research and Clinical Perspectives. Baltimore: Johns Hopkins University Press.

Hoffman, J.E., Landau, B. & Pagani, B. (2003)  Spatial Breakdown in Spatial Construction: Evidence from Eye Fixations in Children with Williams Syndrome. Cognitive Psychology, 45, 260-301.

Jordan, H., Reiss, J. E., Hoffman, J.E., and Landau, B. L. (2002). Intact Perception of Biological Motion in the Face of Profound Spatial Deficits: Williams Syndrome. Psychological Science, 13, 2, 162-167.

Hoffman, J. E. Stages of Processing in Visual Search and Attention. (1999). In Challis, B., & Velichovsky, B. (Eds.) Stratification in cognition and consciousness. Amsterdam/Philadelphia: John Benjamins.

Hoffman, J.E. (1998), Visual attention and eye movements. In H. Pashler (Ed.), Attention. London: University College London Press, 119-154.

Representative Publications

Hoffman, J.E., Landau, B. & Pagani, B. (2003)  Spatial Breakdown in Spatial Construction: Evidence from Eye Fixations in Children with Williams Syndrome. Cognitive Psychology, 45, 260-301

Hoffman, J. E. and Subramanium, B. (1995). The role of visual attention in saccadic eye movements. Perception and Psychophysics, 57, 787-795.

Nigam, A., Hoffman, J.E., and Simons, R.F. (1992). N400 and Semantic Anomaly with Pictures and Words. Journal of Cognitive Neuroscience, 4, 15-22.

Hoffman, J.E., Nelson, B., & Houck, M.R. The role of attentional resources in automatic detection. Cognitive Psychology, 1983, 51, 379-410.

Hoffman, J.E. & Nelson, B.  Spatial selectivity in visual search.  Perception and Psychophysics, l98l, 30, 283-290.

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