Institute of Mental Research
Institute of Mental Research

W. Todd Maddox


PhD, University of California, Santa Barbara

Professor
W. Todd Maddox

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Interests


Cognitive neuroscience of classification, decision-making and attention; translational applications to normal aging, neurological and clinical disorders.

Biography


Was that sound the wind or a wild animal? Does that x-ray show a tumor? Each of these decisions involves categorization. We make hundreds of categorization decisions every day, and in general, we get better with experience. Some of these categorization decisions can be made easily and the strategy can be verbalized. For example, a square is rarely confused with a triangle. These categorization strategies are available to conscious awareness, can be verbalized, and are thought to be frontally mediated.  Other categorization decisions cannot be verbalized. For example, the radiologist can accurately classify whether a tumor is present but will find it difficult to explain exactly how they make that decision. These categorization strategies are not available to conscious awareness, cannot be verbalized and are thought to be striatally-mediated.  Should I invest in stocks or bonds? Should I consume those drugs and alcohol or stay sober? Each of these is an important decision and often involves deciding whether to accept some short-run reward that in the long-run may be sub-optimal or whether to accept some long-run reward by forgoing some short-run reward. These types of decisions are critical to survival, and understanding when and how individuals’ trade off short run and long run rewards is of importance.

A major focus of our research is to examine the computational and neurobiological underpinnings of learning and decision making.  We achieve this goal through a blending of empirical data collection, cognitive neuroscience, and mathematical modeling. The lab has been conducting basic science work in these areas for many years, but over the past decade or so we have begun to extend this work to clinical populations. One area of special interest is depression. Individuals with elevated depressive symptoms often underutilize frontally mediated processes and tend to be more sensitive to punishments than rewards. These factors lead to many straightforward predictions, but also many counterintuitive ones. For example, in a recent paper (Maddox, Chandrasekaran, Smayda, Yi, Koslov, & Beevers, 2014, Cortex) we show that individuals with elevated depressive symptoms are faster to learn non-native speech categories than individuals with low levels of depressive symptoms because the task is one that does not rely heavily on frontal processes. In addition, in two recent studies (Beevers, Worthy, Gorlick, Nix, Chotibut & Maddox, 2013, Psychiatry Research; Maddox, Gorlick, Worthy & Beevers, 2012, Cognition) we showed that individuals with elevated depressive symptoms are poor decision makers when the goal is to maximized long-run gains, but are no worse or are better than individuals with low levels of depressive symptoms when the goal is to minimize long-run losses. A number of other lines of research are ongoing.

Publications


Maddox, W.T. & Zeithamova, D. (2006) Dual task interference in perceptual category learning. Memory & Cognition, 34(2), 387-398.

Markman, A., Maddox, W.T. & Worthy, D. (2006) Choking and excelling under pressure. Psychological Science, 17(11), 944-948. 

Maddox, W.T. & Ashby, F. (2005) Human category learning. Annual Review of Psychology, 56:149-78.

Filoteo, J., Maddox, W.T.,  Salmon, D. & Song, D. (2005) Information-integration Category Learning in Patients with Striatal Dysfunction. Neuropsychology. 19(2), 212-222.

Maddox, W.T. & Ing, A. (2005) Delayed feedback disrupts information-integration but not rule-based category learning. Journal of Experimental Psychology: Learning, Memory & Cognition. 31(1), 100-107.

Maddox, W.T., Aparicio, P., Marchant, N. & Ivry, R. (2005) Rule-based category learning is impaired in patients with Parkinson's disease but not patients with cerebellar disorders. Journal of Cognitive Neuroscience. 17(5), 707-723.

Filoteo, J., Maddox, W.T., Simmons, A., Ing, A., Cagigas, X., Matthews, S. & Paulus, M.P. (2005) Cortical and subcortical brain regions involved in rule-based category learning. Neuroreport. 16(2), 111-115.

Filoteo, J., Maddox, W.T., Ing, A., Zizak, V. & Song, D. (2005) The Impact of Irrelevant Dimensional Variation on Rule-Based Category Learning in Patients with Parkinson's Disease. Journal of the International Neuropsychological Society. 11, 503-513.

Filoteo, J. & Maddox, W.T.  (2004) A quantitative model-based approach to examining aging effects on information-integration category learning. Psychology and Aging. 19(1), 171-182.

Maddox, W.T. & Ashby, F. (2004) Dissociating explicit and procedural-learning based systems of perceptual category learning. Behavioral Processes. 66, 309-332.

Maddox, W.T., Ashby, F., Ing, A. & Pickering, A. (2004) Disrupting feedback processing interferes with rule-based but not information-integration category learning. Memory & Cognition. 32(4), 582-591.

Maddox, W.T. & Bohil, C. (2004) Probability matching, accuracy maximizing and a test of the optimal classifier's independence asumption in perceptual categorization. Perception & Psychophysics . 66(1), 104-118.

Maddox, W.T., Filoteo, J., Hejl, K. & Ing, A. (2004) Category Number Impacts Rule-Based but not Information-Integration Category Learning: Further Evidence for Dissociable Category Learning Systems. Journal of Experimental Psychology: Learning, Memory & Cognition. 30, 227-235.

Bohil, C. & Maddox, W.T.  (2003) A test of the optimal classifier's independence assumption in perceptual categorization. Perception & Psychophysics, 65, 478-493.

Maddox, W.T. & Bohil, C. (2003) A theoretical framework for understanding the effects of simultaneous base-rate and payoff manipulations on decision criterion learning in perceptual categorization. Journal of Experimental Psychology: Learning, Memory & Cognition, 29, 307-320.

Maddox, W.T., Bohil, C. & Dodd, J. (2003) Linear transformations of the payoff matrix and decision criterion learning in perceptual categorization. Journal of Experimental Psychology: Learning, Memory & Cognition. 29, 1174-1193.

Maddox, W.T. & Dodd, J. (2003) Separating perceptual and decisional attention processes in the identification and categorization of integral-dimension stimuli. Journal of Experimental Psychology: Learning, Memory & Cognition, 29(3), 467-480.

Ashby, F., Maddox, W.T. & Bohil, C. (2002) Observational versus feedback training in rule-based and information-integration category learning. Memory & Cognition, 30, 666-677.

Estes, W. & Maddox, W.T. (2002) On the processes underlying stimulus-familiarity effects on recognition of words and nonwords. Journal of Experimental Psychology: Learning, Memory & Cognition, 28, 1003-1018.

Maddox, W.T. (2002) Learning and attention in multidimensional identification, and categorization: Separating low-level perceptual processes and high-level decisional processesJournal of Experimental Psychology: Learning, Memory & Cognition, 28, 99-115.

Maddox, W.T., Ashby, F. & Waldron, E. (2002) Multiple attention systems in perceptual categorization. Memory & Cognition, 30, 325-339.

Markman, A. & Maddox, W.T. (2002) Classification of exemplars with single and multiple feature manifestations: The case of relevant dimension variation. Journal of Experimental Psychology: Learning, Memory & Cognition, 29, 107-117.

Bohil, C. & Maddox, W.T. (2001) Category discriminability, base-rate, and payoff effects in perceptual categorization. Perception & Psychophysics, 63, 361-376.

Filoteo, J, Maddox, W.T. & Davis, J. (2001) A possible role of the striatum in linear and nonlinear categorization rule learning: Evidence from patients with Huntington's disease. Behavioral Neuroscience, 115, 786-798.

Filoteo, J., Maddox, W.T. & Davis, J. (2001) Quantitative modeling of category learning in amnesiac patients. Journal of the International Neuropsychological Society, 7, 1-19.

Maddox, W.T. (2001) Separating perceptual processes from decisional processes in identification and categorization. Perception & Psychophysics, 63, 1183-1200.

Maddox, W.T. & Bohil, C. (2001) Feedback effects on cost-benefit learning in perceptual categorization. Memory & Cognition, 29, 598-615.

Maddox, W.T. & Dodd, J. (2001) On the relation between base-rate and cost-benefit learning in simulated medical diagnosis. Journal of Experimental Psychology: Learning, Memory & Cognition, 27, 1367-1384.

Maddox, W.T. & Filoteo, J. (2001) Striatal contribution to category learning: Quantitative modeling of simple linear and complex non-linear rule learning in patients with Parkinson's disease. Journal of the International Neuropsychological Society, 7, 710-727.

Maddox, W.T., Molis, M. & Diehl, R. (2001) Generalizing a neuropsychological model of visual categorization to auditory categorization of vowels. Perception & Psychophysics, 64, 584-597.

Maddox, W.T. & Bogdanov, S. (2000) On the relation between decision rules and perceptual representation in multidimensional perceptual categorization. Perception & Psychophysics, 62, 984-997.

Maddox, W.T. & Bohil, C. (2000) Costs and benefits in perceptual categorization. Memory & Cognition, 28, 597-615.

Filoteo, J. & Maddox, W.T. (1999) Quantitative modeling of visual attention processes in patients with Parkinson's Disease: Effects of stimulus integrality on selective attention and dimensional integration. Neuropsychology, 13, 206-222.

Maddox, W.T. (1999) On the dangers of averaging across observers when comparing decision-bound models and generalized context models of categorization. Perception & Psychophysics, 61, 354-374.

Maddox, W.T. & Ashby, F. (1998) Selective attention and the formation of linear decision bounds: Commentary on McKinley and Nosofsky. Journal of Experimental Psychology: Human Perception and Performance, 24, 301-321.

Maddox, W.T., Ashby, F. & Gottlob, L.R. (1998) Response time distributions in multidimensional perceptual categorization. Perception & Psychophysics, 60, 620-637.

Maddox, W.T. & Bohil, C. (1998) Base-rate and payoff effects in multidimensional perceptual categorization. Journal of Experimental Psychology: Learning, Memory, and Cognition, 24, 1459-1482.

Maddox, W.T. & Bohil, C. (1998) Overestimation of base-rate differences in complex perceptual categories. Perception & Psychophysics, 60, 575-592.

Maddox, W.T. & Filoteo, J. (1998) Effects of stimulus integrality on visual attention in older and younger adults: A quantitative model-based analysis. Psychology and Aging, 13, 472-485.

Maddox, W.T. & Ashby, F. (1998) Stimulus categorization. Academic Press (pgs. 251-301).

Maddox, W.T. & Estes, W. (1997) Direct and indirect stimulus-frequency effects in recognition. Journal of Experimental Psychology: Learning, Memory, and Cognition, 23, 539-559.

Ashby, F., Prinzmetal, W. & Ivry, R. & Maddox, W.T, (1996) A formal theory of feature binding in object perception. Psychological Review, 103, 165-192.

Maddox, W.T. & Ashby, F. (1996) Perceptual separability, decisional separability, and the identification-speeded classification relationship. Journal of Experimental Psychology: Human Perception and Performance, 22, 795-817.

Maddox, W.T., Filoteo, J., Delis, D. & Salmon, D. (1996) Visual selective attention deficits in patients with Parkinson's disease: A quantitative model-based approach. Neuropsychology, 10, 197-218.

Estes, W & Maddox, W.T. (1995) Interactions of stimulus attributes, base rate, and feedback in recognition. Journal of Experimental Psychology: Learning, Memory, and Cognition, 21, 1075-1095.

Maddox, W.T. (1995) Base-rate effects in multidimensional perceptual categorization. Journal of Experimental Psychology: Learning, Memory, and Cognition, 21, 288-301.

Ashby, F. & Maddox, W.T. (1994) A response time theory of separability and integrality in speeded classification. Journal of Mathematical Psychology, 38, 423-466.

Ashby, F., Maddox, W.T. & Lee, W. (1994) On the dangers of averaging across subjects when using multidimensional scaling or the similarity-choice model. Psychological Science, 5, 144-151.

Maddox, W.T., Prinzmetal, W., Ivry, R. & Ashby, F. (1994) A probabilistic multidimensional model of location information. Psychological Research, 56, 66-77.

Ashby, F. & Maddox, W.T. (1993) Relations between prototype, exemplar, and decision bound models of categorization. Journal of Mathematical Psychology, 37, 372-400.

Maddox, W.T. & Ashby, F. (1993) Comparing decision bound and exemplar models of categorization. Perception & Psychophysics, 53, 49-70.

Ashby, F. & Maddox, W.T. (1992) Complex decision rules in categorization: Contrasting novice and experienced performance. Journal of Experimental Psychology: Human Perception and Performance, 18, 50-71.

Maddox, W.T. (1992) Perceptual and decisional separability.  In F.G. Ashby (Ed.), Multidimensional Models of Perception and Cognition. (pgs. 147-180). Erlbaum: Hillsdale, NJ.

Ashby, F. & Maddox, W.T. (1991) A response time theory of perceptual independence. In J.P. Doignon and J.C. Falmagne (Eds.) Mathematical psychology: Current developments. (pgs. 389-413). Springer-Verlag.

Ashby, F. & Maddox, W.T. (1990) Integrating information from separable psychological dimensions. Journal of Experimental Psychology: Human Perception and Performance, 16, 598-612.

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