Professor Tom Freeman BSc PhD Birm

Professor Tom Freeman

BSc PhD Birm

Professor

School of Psychology

Email:
freemant@cardiff.ac.uk
Telephone:
+44 (0)29 2087 4554
Location:
Tower Building, 70 Park Place, Cardiff, CF10 3AT

Research summary

Images move mainly because we do.  Simple actions like rotating the eye or head make stationary objects sweep  across the retina, while in hearing, head movements cause dynamic changes in auditory  cues to location. Our own movements therefore create some very basic problems  for the perceptual brain – how do the vision and hearing know whether we are  moving, objects are moving, or both? One solution the brain adopts is to use  signals from the motor system to help interpret incoming sensory information during  self-movement.

My work investigates the  fundamental mechanisms that drive this process, using a variety of techniques.  These include measuring how well we control eye and head movements, how  successful we are at judging  moving  objects that are seen and heard, and which regions of the brain are active as  we do so. The findings help test and develop key theories in perception, in  particular how sensory evidence and prior knowledge are integrated. Some of the  results are applied to various clinical conditions, such as schizophrenia, nystagmus  and Huntington’s disease.

Teaching summary

Levels 1 and 2:

I give a variety of tutorials as Levels 1 and 2 on perception, cognition,   developmental and abnormal psychology (supporting PS1014, PS2003, PS2008,   PS2009). At Level 2, I teach one half of the Perception module (PS2009),   concentrating on 'The Other senses’. I also run practicals in Perception.

Level 3:

I teach and coordinate the 'Vision and Action’ module, where we examine our   current understanding of visual perception during motor activity and how visual   perception helps support self-motion. I supervise projects on a number of topics in   perception.

Undergraduate education

1984-1987 BSc Hons (2i), School of Psychology, University of Birmingham

Postgraduate education

1987-1990 Doctoral degree supervised by Dr M.G. Harris, School of Psychology,   University of Birmingham

Employment

2012 – present day Professor, School of Psychology,  Cardiff  University

2008-2012: Reader in Psychology,  School of Psychology, Cardiff University

2003 - 2008:  Senior Lecturer, School of Psychology, Cardiff University

1999 - 2003:  Lecturer, School of Psychology, Cardiff University

1997 - 1999:  Fixed-term lecturer, School of Psychology, Cardiff   University

1995 - 1997:  Research Fellow with Prof. M. S. Banks, School of Optometry,   University of California, Berkeley

1992 - 1995:  Research Fellow with Prof. M. A. Georgeson, Department of   Vision Sciences, Aston University

1991 - 1992:  Lecturer, School of Psychology, University of Birmingham

1990 - 1991:  Research Associate with Prof. G.W. Humphreys, School of   Psychology, University of Birmingham

Honours and awards

Awards/external committees

External  panel member, Liverpool Hope University Psychology Dept. Review, 2014

Expert  reviewer for Bournemouth University mock-REF, School of Psychology, 2013

EPSRC peer-review college (2006-present day).

Editor, Perception

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Research topics and related papers

1. Combining prior expectations and uncertainty to explain motion   illusions during pursuit.

Your browser does not support the video tag. As the pictures of  Charlie above demonstrate, smooth eye pursuit adds motion to the retinal image  – movement on the retina doesn’t 'line-up’ with the motion of objects in the  world. Hence, when we track Charlie (right picture), the cupboard moves in the  image, and he is more or less stationary. One way the visual brain solves this  problem is to add estimates of eye velocity to estimates of image motion, which  gives an estimate of the 'real’ motion. This process doesn’t always work  accurately - observers often misperceive velocity when they move their eyes.  Thus, pursued stimuli appear slower (Aubert-Fleishl phenomenon), stationary  objects appear to move (Filehne illusion), the perceived direction of objects  moving on a different trajectory to the eye is distorted and self-motion veers  away from its true path (e.g. the slalom illusion). Each of these illusions  demonstrate that eye speed is often underestimated with respect to image speed,  a finding that many authors have taken as evidence of early sensory signals  that differ in accuracy. In this project we tested an alternative, based on the  idea that perceptual estimates are increasingly influenced by prior  expectations when motion signals become more uncertain. Most objects are  stationary or move slowly; hence the visual system’s prior expectation is a  distribution that peaks at 0 (represented by the black line in the movie above).  Motion signals are represented by the red line, with their uncertainty (=  precision) captured by the width of the distribution shown. Perceived speed is  based the combination of the two (they are multiplied together according to  Bayes rule to yield the blue distribution). As motion signals become more  uncertain, the blue distribution moves towards the prior. Hence perceived speed  slows down.

Freeman, T. C. A.,  Champion, R. A. and Warren, P. A. (2010). A Bayesian model of perceived  head-centered velocity during smooth pursuit eye movement. Current  Biology, 20(8), 757-762. (10.1016/j.cub.2010.02.059)

2. Auditory compensation for head rotation

A fundamental yet almost entirely overlooked problem in  hearing is how auditory motion cues that occur 'at the ears’ are interpreted  when the head moves. The motivation for this project is based on the idea that  the world is largely stationary, containing only a few moving objects, while  the head continually moves (just as the eyes do in vision – see above). At the  ear, therefore, the auditory cues to motion are dominated by self-motion not  object motion. A considerable amount is known about how retinal image motion is  integrated with 'extra-retinal signals’ that are based on motor and vestibular  system activity and provide information about eye and head movement. Continuing  the analogy, we are currently exploring whether the auditory system uses equivalent  'extra-cochlear’ information to interpret dynamic changes in acoustic images.

To explore this issue, we use a technique based on linking  moving sounds with real-time measurements of head rotation. The technique  allows us to determine a simple, yet fundamental, assessment of auditory motion  perception, namely the degree to which a sound must rotate around the listener  in external space in order to appear stationary. Like vision, we discover that  hearing is able to compensate for this type of self-movement quite well, but  there is a persistent error that we provide evidence for over the course of two  experiments. This perceptual error is the auditory analogue of the Filehne  illusion in vision, first described almost 100 years ago, in which a static object  appears to move against a smooth pursuit eye movement. We are currently  investigating whether Bayesian models like that described above could account  for the auditory Filehne illusion.

In collaboration with John Culling (Cardiff),  Owen Brimijoin (MRC Institute of Hearing, Glasgow Section) and Michael Akeroyd  (MRC Institute of Hearing, Nottingham).

3. Oculomotor control: precision and accuracy as a function of   age

Click here for an   interview with Tom Freeman on this and related ageing projects

We know that as we grow older, the accuracy of our tracking eye   movements decreases. However, little is know about how the precision   (variability) of eye movements in either young or older observers. In this   project we developed a new analysis that allowed us to account for two types of   precision – short-duration 'shake’ and longer-duration 'drift’. We found that   older observers were less precise at faster eye speeds. We also found that the   way the two precision measures depended on speed differed with the type of eye   movement our observers made. When they made reflexive eye movements, shake was   largely independent of speed and resembled the variability measured during   fixation. When they made deliberate eye movements, both shake and drift   increased with speed. This suggests that the two different types of eye   movements do not share the same noise source.

Kolarik, A.J., Margrain, T.H., & Freeman, T.C.A. (2010). Precision and   accuracy of ocular following: Influence of age and type of eye movement. Experimental Brain Research. 201, 271-282.

Funded by BBSRC/EPSRC 'Strategic Promotion of Ageing Research Capacity’   (SPARC) initiative

Recent Funding

Wellcome  ISSF (2016), £38,601
K Singh, J Walters, T  Freeman & J Zhang “Neurophysiologically- informed models  and  machine learning classification of  task-driven and
resting state oscillatory dynamics in  schizophrenia”.

Fight  for Sight / Nystagmus network (2013), £14,350
J Erichsen &  T Freeman  “Understanding  the basis for oscillopsia in nystagmus  to provide a basis for treatment”

JE  Williams Endowment studentship, £  55,235
J Erichsen & T  Freeman “Evaluating eye  movements as biomarkers for monitoring  the progression of Huntington’s Disease to  facilitate early
intervention and clinical management.”

Wellcome  ISSF (2013), £12,152
P  Sumner, S.K. Rushton, T.C.A. Freeman  “Improving  rehabilitation of visual vertigo through understanding the visual triggers”

MRC  (2013), £924,429
K  Singh, T.C.A. Freeman, J Walters, L Wilkinson  “Defining  the disturbances in cortical glutamate and GABA function in psychosis, its origins and  consequences”

Royal  Society International Travel Grant (2010), £4000                                                    
T.C.A.  Freeman “Auditory  and audio-visual motion perception during  eye movement and head rotation”

Wellcome  Trust (2007), £135,  799
T.C.A. Freeman  “Visual motion sensitivity during  eye movement: Investigating the interaction  between retinal and extra-retinal noise”

BBSRC/EPSRC  SPARC initiative (2006), £37,230
T.C.A. Freeman & T.H.  Margrain“Age, eye movement and motion  perception”

Research group

John Culling (active hearing)

Krish Singh (schizophrenia, GABA/gamma and orientation perception; brain imaging and active  motion perception)

Petroc  Sumner (OKN, smooth pursuit and saccades; infantile nystagmus)

Research collaborators

Owen Brimijoin (MRC Institute of  Hearing, Scottish section), Michael Akeroyd (MRC. Institute of Hearing,  Nottingham)

David  Alais, Simon Carlile (University of Sydney): Auditory motion perception

Rebecca Champion / Paul Warren (University of Manchester): Bayesian models of head-centred motion perception

Marc Ernst / Jan Souman (Max Planck Institute,  Tubingen): Motion perception during walking

Jon  Erichsen (infantile nystagmus, Huntington’s  disease)

Tom  Margrain (age, eye movement and motion  sensitivity)

Postgraduate research interests

I am happy to discuss PhD projects in any area of psychophysics and/or motor   control, especially those that relate visual performance with motor activity.   Current PG projects include: age, eye movement and motion sensitivity;   interaction between retinal and extra-retinal motion afterefffects;   extra-retinal signatures in MEG and fMRI.

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

James  Brawn
Lee  McIlreavy

Past projects

Previous students

Laura Whitlow, Graduated 2015
James Harrison, Graduated 2014
Ben Dunkley, Graduated  2012
Emer O’Connor, Graduated 2011
Rhys Davies, Graduated 2011
Joni Karanka, Graduated  2009
Rhodri Woodhouse Graduated 2009
Jenny Naji, Graduated 2004
Alastair Barrowcliff, Graduated 2003