Professor Dominic M Dwyer - BSc Sydney PhD Cambridge

Professor

Research group:
Neuroscience
Email:
DwyerDM@cardiff.ac.uk
Telephone:
+44(0)29 2087 6285
Location:
Tower Building, Park Place

Research summary

Animals, including humans, readily learn links between events that occur close together in time and space. The classic example from animal learning comes from Pavlov’s demonstration that dogs that were fed immediately after hearing a bell began to salivate in advance of the food when the bell was rung. This can be described in terms of the dogs learning an association between the mental representation of the bell, and the mental representation of food, such that hearing the bell activates the representation of food (and that in turn drives the relevant responses). One major strand of my research examines the mechanisms by which associations are formed and influence behaviour in both humans and other animals. This has included an exploration of some, seemingly unlikely, phenomena where associative learning may play a crucial role: for example in learning how to distinguish similar faces, how animals deal with problems of causation, or how people learn their likes and dislikes.

A second major strand of my research involves the assessment of hedonic responses in rodents. Animal models are of critical importance in investigating the underlying biological contributions to many human disorders such as depression or schizophrenia. To fully understand these animal models we require ways to assess how animals feel, as well as how they think. As it happens, a detailed examination of the way in which rodents drink is particularly informative with respect to how much they like what they are drinking (e.g. rats tend to produce few, but rather long, bouts of licks when they like the solution they are drinking but the length of the bouts decreases, while the number of bouts can increase, with less palatable solutions). Research in my lab is currently using this technique to investigate how animals learn to like and dislike particular foods and also how such hedonic processes are affected in animals models of human disorders, in particular schizophrenia, depression and dementia.

Teaching summary

I am the chair of the undergraduate exam boards.

Levels 1 and 2: I teach introductory lectures on statistics and biological psychology (PS1015 and PS2017). I also run cognitive practicals and give tutorials on social, perception, cognition and abnormal/clinical psychology (supporting PS2007, PS2003, PS2009, PS2018).

Level 3: I supervise projects on a variety of topics including face perception and the learning and expression of food preferences.

Selected publications (2014 onwards)

 

Online publications

Full list of publications

 

Research topics and related papers

Much of my research has focused on exploring the contribution of associative processes (and their limits) to forms of learning that might be considered to be “unusual” in some way (e.g. taste aversion learning, conditioned flavour preferences, and perceptual learning). The four projects outlined below provide a sample of some of this continuing research.

Perceptual learning:

The ability to distinguish between very similar stimuli improves with exposure to those stimuli, a process that can generally be described as perceptual learning. Critically, it is not just the total amount of stimulus exposure that matters, but the structure of that exposure. Although many explanations for this effect have been offered, many struggle to explain the fact that simultaneous exposure to a pair of cues both allows excitatory associations to form between them and supports improved discrimination (e.g. Mundy, Honey, & Dwyer, 2007). Therefore, we have been exploring the idea that differential levels of habituation during initial exposure to features that are unique to a particular stimulus as compared to features that are shared between stimuli will bias the stored representations of those stimuli in ways that support accurate subsequent processing – that is, the change in stored representations supports the improvement in discrimination while associations between these stored representations support the excitatory learning.

The idea of habituation-based changes in the quality of a representation is not a mechanism that should be specific to any particular class of stimulus. Indeed we have seen similar results with stimuli ranging from odours and flavours (e.g. Mundy, Dwyer, & Honey, 2006) to abstract checkerboard stimuli (e.g. Mundy, Honey, & Dwyer, 2009). However, we have also observed that the neural substrate of perceptual learning is influenced by stimulus type. In particular, perceptual learning with faces seems to recruit cortical areas not used for perceptual learning with checkerboards (e.g. Mundy, Honey, Downing, Wise, Graham, & Dwyer, 2009). The combination of behavioural and neural results raises the possibility that there might be a conservation of cognitive mechanisms across different brain regions specific to different stimulus classes.

The majority of my research has examined situations where subjects (people or other animals) are exposed to all of the stimuli that they are to distinguish at test. However, the opportunity to compare a target stimulus to other comparison stimuli during exposure appears to produce better processing of that target even if testing requires it to be distinguished from new distractors (e.g. Dwyer & Vladeanu, 2009). The generality of this effect, and the practical implications it has for learning to recognise new faces, is an ongoing topic of investigation.

Preference and aversion learning:

Animals readily learn to prefer flavours that are experienced alongside already pleasant tastes or that predict the arrival of nutrients in the gastric system. I addition, they readily learn to avoid flavours paired with unpleasant consequences. There has been much debate over whether these processes of preference and aversion learning can be explained within a more general associative framework or whether they require special principles to explain their apparent “unique” properties. My own view is that general associative mechanisms are sufficient to explain both acquired preference and aversions but that the particular features of the cues involved, and the way that animals interact with them (e.g. the fact that flavours are normally experienced by active consumption), can explain the bulk of research in this area (e.g. Dwyer, 2005; Dwyer & Quirk, 2008) – although it should be said that such “general associative mechanisms” appear to allow for learning based on the representation of absent stimuli to a far greater degree than is often supposed (e.g. Dwyer, 2003). In addition to affecting the amount of consumption both preference and aversion learning appears to change animals hedonic reactions to the cue flavours, although this change in hedonic reaction does not appear to be particularly persistent (e.g. Dwyer, 2009; Dwyer, Pincham, Thein, & Harris, 2009)

Representation and reasoning in rats:

My early research on learnt preferences and aversions has highlighted the degree to which new learning can be supported by the representations of particular foods in the absence of the foods themselves (e.g. Dwyer, 1999; Dwyer, Mackintosh, & Boakes, 1998) and that such “representation-mediated” learning can be explained with only minor modifications to the associative processes held to explain learning about stimuli that are actually present (e.g. Dwyer, 2003). This is particularly interesting because the performance of animals in these tasks could be characterised as reflecting a reasoning process: for example, when animals receive initial pairings of two cues with a palatable outcome then exposure to one flavour alone tends to raise the preference for the remaining flavour, something the “looks” like the rats are reasoning that their initial experience was disambiguated by learning that the first flavour alone did not predict the positive consequence and so the second flavour must have done so! Indeed, the idea that relatively simple processes might explain seemingly complicated behaviours in human and non-human animals alike is one of the continuing themes of my research (e.g. Dwyer, Starns, & Honey, 2009; Dwyer & Burgess, 2011). That is not to say that I think that animals (including humans) are simply automata following simple associative rules, but that before asserting that more complicated processes are at work we should explore the contributions of simpler mechanisms first. The exploration of the limits of associative models as explanations for “rational” behaviour in rats is an ongoing topic of investigation.

Hedonic responses in animal models of disorders:

Although changes in affective responses are a key feature of a number of disorders (e.g. anhedonia in depression or schizophrenia) it is a particular problem to assess the degree to which animal models of these disorders produce the same hedonic changes. This problem is particularly acute because animal models are extensively used in the development of novel pharmacological therapeutic techniques. One way to investigate an animal’s hedonic reaction is to examine the manner in which it drinks: rodents typically consume fluids in repeated clusters of licks separated by pauses. The number of licks in each cluster has a positive, monotonic relationship with the concentration of palatable solutions such as sucrose and a negative monotonic relationship with the concentration of unpalatable solutions such as quinine. That is, an increases and decreases in lick cluster size reflect increases and decreases in hedonic evaluation respectively. My initial use of this technique was in the context of manipulating the flavour itself in terms of the acquisition of flavour preferences and aversions (see above and also Dwyer, Boakes, & Hayward, 2008) but more recently I have been examining the consequences of manipulating the state of the animal itself. In particular, one of my recent PhD students (Emma Lydall) has been examining animal models of schizophrenia based on either acute or chronic administration of NMDA antagonists such as PCP. Despite the fact that PCP-based models are claimed to mimic the full range of schizophrenia symptoms she has found no evidence that they actually produce any identifiable analogue of the anhedonia as is described for humans with schizophrenia (e.g. Lydall, Dwyer, & Gilmour, 2010). The exploration of the affective and cognitive effects of animal models of psychosis, dementia and affective disorders is an ongoing topic of investigation.

Research collaborators

Professor Robert Boakes (Psychology, University of Sydney)

Dr Tom Freeman (Psychology, Cardiff University)

Professor Kevin Fox (Biosciences, Cardiff University)

Professor Kim Graham (Psychology, Cardiff University)

Professor Justin Harris (Psychology, University of Sydney)

Dr Mark Haselgrove (Psychology, University of Nottingham)

Professor Robert Honey (Psychology, Cardiff University)

Dr Michael Lewis (Psychology, Cardiff University)

Dr Matthew Mundy (Psychology, Monash University)

Postgraduate research interests

My theoretical interests are broadly focused on the associative and neural mechanisms underpinning learning, memory and preference. Recently, this has included a particular emphasis on the limits of associative accounts of behaviour due to the speculation that rats may be capable of causal reasoning. In empirical terms I have a particular expertise in the assessment of hedonic behaviours in rodents, something that can be applied to the effects of both purely behavioural manipulations (e.g. the examination of how the context in which a substance is consumed can affect how it is perceived) and those of a more applied nature (e.g. the possibility that palatability assessment might allow for the modelling of symptoms such as anhedonia that are a feature of mental disorders such as depression or the assessment of the mechanisms underpinning the disordered eating seen in mouse models of Prader-Willi syndrome). Another strand of my research has examined the contribution of general neural and associative mechanisms to perceptual learning as well as how these general mechanisms might contribute to the special case of face processing.

I am interested in discussing the possibility of supervising research projects related to any of my theoretical interests or areas of empirical expertise.

If you are interested in applying for a PhD, or for further information regarding my postgraduate research, please contact me directly (contact details available on the 'Overview' page), or submit a formal application here.

Current students

John Riordan: (co-supervised by Professor John Pearce) John began his PhD in 2015 and is invesitgating the degree to which flavour preferences and aversions reflect “special” learning mechanisms.  His research is supported by the Leverhulme Trust and Giract.

Adam Brelsford: (co-supervised by Professor Mark Good, Dr Emma Kidd, Dr Rhian Thomas) Adam began his PhD research in 2015 examining affective and cognitive deficits in mouse models of dementia.

Rebecca Wright: (co-supervised by Dr Gary Gilmour of Eli Lilly & Company). Rebecca was awarded a BBSRC industrial CASE studentship (sponsored by Eli Lilly & Company) and began her PhD research in 2011. The general theme for Rebecca’s research is the examination of the affective and cognitive effects of animal models of psychosis and affective disorders.

Previous students

Katy Burgess: (co-supervised by Professor Robert Honey) Katy began her PhD research in 2009 examining cognitive and representational processes in rats. This work entailed a critical examination of the hypothesis that rats are capable of causal reasoning and an investigation of whether the “causal binding” phenomenon can be observed in rats as well as in humans

Scott Jones: (co-supervised by Dr Michael Lewis) Scott began his PhD research in 2009 examining the contribution of perceptual learning to the process by which faces become familiar. In particular investigated the effects of the opportunity to compare a new face to other faces on the speed and quality of learning.

Rebecca Wright: (co-supervised by Dr Gary Gilmour of Eli Lilly & Company). Rebecca was awarded a BBSRC industrial CASE studentship (sponsored by Eli Lilly & Company) and began her PhD research in 2011. The general theme for of Rebecca’s research was be an examination of the affective and cognitive effects of animal models of psychosis and affective disorders.

Emma Lydall: (co-supervised by Dr Gary Gilmour of Eli Lilly & Company). Emma was awarded a BBSRC industrial CASE studentship (sponsored by Eli Lilly & Company) and began her PhD research in 2007. The main focus of Emma’s research was the examination of whether animal models of schizophrenia extend to the entail a reduction in the hedonic response associated with pleasant stimuli (such anhedonic responses have been identified as a key symptom in schizophrenia and other disorders such as depression). In addition Emma has also contributed to the examination of hedonic processes in purely behavioural situations, including a direct demonstration that rats prefer the taste of sucrose when they have had to work hard for it than when they have not.

Dr Matthew Mundy: Currently a lecturer at Monash University in Australia, Matthew was previously employed as a WICN research fellow in the period immediately following his PhD . The main focus of Dr Mundy’s PhD research was an examination of the effects of exposure schedule in perceptual learning with both faces and non-face stimuli.

David Ross: (co-supervised with Dr Michael Lewis). Currently a Post-doc at Vanderbilt University, David’s PhD (which was passed entirely without corrections) investigated the nature of the representation of faces with a particular focus on comparing norm- and exemplar-based models.

Undergraduate education

1995: BSc (Honours Class 1, Medal) in Psychology: University of Sydney.
Empirical thesis title - Activity-Based Anorexia.
Theoretical thesis title - The nature of number and measurement in psychology.
Also studied; Statistics, Mathematics, Law, Chemistry.

Postgraduate education

1999: PhD: Department of Experimental Psychology, University of Cambridge.
Thesis title - Learning about absent stimuli. Supervised by Professor N.J. Mackintosh.

Awards/external committees

2011: Delivered the 18th Experimental Psychology Society Prize Lecture

2000: Emanuel Miller Prize for the Philosophy of Science

1996: Cambridge Commonwealth Trust Packer Scholarship for graduate study.

1995: University Medal for Psychology

Dick Thomson Prize for Psychology

Australian Psychological Society Prize for Psychology Honours.

Employment

2012 to present: Reader, School of Psychology, Cardiff University.

2007 to 2012: Senior Lecturer, School of Psychology, Cardiff University.

2003 - 2007: Lecturer, School of Psychology, Cardiff University.

2002 - 2003: Research Associate, Cardiff University.

1999 - 2002: Junior Research Fellow, Churchill College, Cambridge.

Other Activities

Journals: I am an associative editor for The Quarterly Journal of Experimental Psychology. I have reviewed for over 15 different journals (including Current Biology, The Journal of Neuroscience, The European Journal of Neuroscience) and am an associate of the BBS. Grant Reviewing: BBSRC, ESRC, and the City University of New York. Invited Talks: I have been invited to give lectures at many institutions both within Britain (e.g. The Zangwill lecture at the University of Cambridge and at Eli Lilly & Company) and internationally (e.g. The University of Sydney and The University of NSW). Thesis Examination: I have examined both MSc and PhD theses both internally and externally (e.g. for the University of Sydney and the University of NSW).