Dr Tom Freeman - BSc PhD Birm
Overview
Research Group:
Perception & Action
Location: Tower Building, Park Place
Email: FreemanT@cardiff.ac.uk
Telephone: +44(0)29 208 74554
Research Summary
Images move mainly because we do. Simple actions like tracking a moving target by eye, make stationary objects sweep across the retina. More complex actions, like walking and driving, cause the visual scene to smoothly expand in the image. Our own movements therefore create some very basic problems for the brain – how does the visual system 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 visual information as we move.
My work investigates the fundamental mechanisms that drive this process, using a variety of techniques. These include measuring how well we can control our eye movements, how successful we are at judging object motion and which regions of the brain are active as we do so.
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 action. I supervise projects on a number of topics in perception.
Selected Publications (2008 onwards)
Dunkley, B.T., Freeman, T.C.A., Muthukumaraswamy, S.D., & Singh, K.D. (in press). Cortical oscillatory changes in human MT+ underlying smooth pursuit eye movements. Human Brain Mapping.
Davies, J.R., & Freeman, T.C.A. (2011). Simultaneous adaptation to non-collinear retinal motion and smooth pursuit eye movement. Vision Research, 51, 1637-1647. [pdf]
Souman, J.L., Freeman, T.C.A., Eikmeier, V., & Ernst, E.O. (2010). Humans do not have direct access to retinal flow during walking. Journal of Vision, 10(11):14, 1–12. [pdf]
O’Connor, E., Margrain, T.H., & Freeman, T.C.A. (2010). Age, eye movement and motion discrimination. Vision Research, 50, 2588-2599. [pdf]
Champion, R.A., & Freeman, T.C.A. (2010). Discrimination contours for the perception of head-centred velocity. Journal of Vision, 10(6):14, 1–9. [pdf]
Freeman, T.C.A., Champion, R.A., & Warren, P.A. (2010). A Bayesian model of perceived head-centred velocity during smooth pursuit eye movement. Current Biology, 20, 757-762. [pdf]
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. [pdf]
Edden, R.A.E., Muthukumaraswamy, S.D., Freeman, T.C.A., & Singh, K.D. (2009). Orientation discrimination performance is predicted by GABA concentration and gamma oscillation frequency in human primary visual cortex. Journal of Neuroscience, 29, 15721-15726. [pdf]
Freeman, T. C. A., Champion, R. A., Sumnall, J. H., & Snowden, R. J. (2009). Do we have direct access to retinal image motion during smooth pursuit eye movements? Journal of Vision, 9(1):33, 1-11. [pdf]
Souman, J.L., & Freeman, T.C.A. (2008). Motion perception during sinusoidal smooth pursuit eye movements: Signal latencies and non-linearities. Journal of Vision, 8, 14, 1-14. [pdf]
Publications
Online Publications
Click on my Researcher ID badge for electronic information about my publications:
Full List of Publications
Forthcoming
Dunkley, B.T., Freeman, T.C.A., Muthukumaraswamy, S.D., & Singh, K.D. (in press). Cortical oscillatory changes in human MT+ underlying smooth pursuit eye movements. Human Brain Mapping.
2011
Davies, J.R., & Freeman, T.C.A. (2011). Simultaneous adaptation to non-collinear retinal motion and smooth pursuit eye movement. Vision Research, 51, 1637-1647. [pdf]
2010
Souman, J.L., Freeman, T.C.A., Eikmeier, V., & Ernst, E.O. (2010). Humans do not have direct access to retinal flow during walking. Journal of Vision, 10(11):14, 1–12. [pdf]
O’Connor, E., Margrain, T.H., & Freeman, T.C.A. (2010). Age, eye movement and motion discrimination. Vision Research, 50, 2588-2599. [pdf]
Champion, R.A., & Freeman, T.C.A. (2010). Discrimination contours for the perception of head-centred velocity. Journal of Vision, 10(6):14, 1–9. [pdf]
Freeman, T.C.A., Champion, R.A., & Warren, P.A. (2010). A Bayesian model of perceived head-centred velocity during smooth pursuit eye movement. Current Biology, 20, 757-762. [pdf]
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. [pdf]
2009
Edden, R.A.E., Muthukumaraswamy, S.D., Freeman, T.C.A., & Singh, K.D. (2009). Orientation discrimination performance is predicted by GABA concentration and gamma oscillation frequency in human primary visual cortex. Journal of Neuroscience, 29, 15721-15726. [pdf]
Freeman, T. C. A., Champion, R. A., Sumnall, J. H., & Snowden, R. J. (2009). Do we have direct access to retinal image motion during smooth pursuit eye movements? Journal of Vision, 9(1):33, 1-11. [pdf]
2008
Souman, J.L., & Freeman, T.C.A. (2008). Motion perception during sinusoidal smooth pursuit eye movements: Signal latencies and non-linearities. Journal of Vision, 8, 14, 1-14. [pdf]
2007
Freeman, T.C.A. (2007). Simultaneous adaptation of retinal and extra-retinal signals. Vision Research, 47, 3373-3384. [pdf]
Georgeson, M. A., May, K. A., Freeman, T. C. A., & Hesse, G. S. (2007). From filters to features: Scale–space analysis of edge and blur coding in human vision. Journal of Vision, 7(13):7, 1-21. [pdf]
Freeman, T.C.A. (2007). Extra-retinal vision: Firing at will. Current Biology, 17(3), R99-R101. [pdf]
2005
Freeman, T.C.A., & Sumnall, J.H. (2005). Extra-retinal adaptation of cortical motion-processing areas during pursuit eye movements. Proceedings of the Royal Society, Series B: Biological Sciences, 272, 2127-2132. [pdf]
2004
Snowden, R.J., & Freeman, T.C.A. (2004). The visual perception of motion. Current Biology, 14, R828-R831. [pdf]
Naji, J.J., & Freeman, T.C.A. (2004). Perceiving depth order during pursuit eye movement. Vision Research, 44, 3025-3034. [pdf]
Barrowcliff, A.L., Gray, N.S., Freeman, T.C.A., & MacCulloch, M.J. (2004). Eye-movements reduce the vividness, emotional valence and electrodermal arousal associated with negative autobiographical memories. Journal of Forensic Psychiatry & Psychology, 15, 325-345. [pdf]
Freeman, T.C.A. (2004). Motion perception during eye movement: Some questions answered, some that remain. In B. de Graaf (Ed.), Progress in self-motion research. TNO-report, Netherlands.
2003
Freeman, T.C.A., Sumnall, J.H., & Snowden, R.J. (2003). The extra-retinal motion aftereffect. Journal of Vision, 3, 771-779. [pdf]
Sumnall, J.H. & Freeman, T.C.A., & Snowden, R.J. (2003). Optokinetic potential and the perception of head-centred motion. Vision Research, 43, 1709-1718. [pdf]
Barrowcliff, A.L., Gray, N.S., MacCulloch, S, Freeman, T.C.A., & MacCulloch, M.J. (2003). Eye-movement desensitization & reprocessing (EMDR) and the investigatory reflex. British Journal of Clinical Psychology, 42, 289-302
2002
Freeman, T.C.A., Naji, J.J., & Margrain, T.H. (2002). Head-centred motion perception in the ageing visual system. Spatial Vision, 15, 117-127. [pdf]
Freeman, T.C.A., & Sumnall, J.H. (2002). Motion versus position in the perception of head-centred movement. Perception, 31, 603-615. [pdf]
2001
Freeman, T.C.A. (2001) Transducer models of head-centred motion perception. Vision Research, 41, 2741-2755. [pdf]
2000
Freeman, T.C.A., & Fowler, T.A. (2000). Unequal retinal and extra-retinal motion signals produce different perceived slants of moving surfaces. Vision Research, 40, 1857-1868. [pdf]
Freeman, T.C.A., Banks, M.S. & Crowell, J.A (2000). Extra-retinal & retinal amplitude and phase errors during Filehne illusion and path perception. Perception & Psychophysics, 62, 900-909. [pdf]
1999
Freeman, T.C.A. (1999). Path perception and Filehne illusion compared: model and data. Vision Research, 39, 2659-2667. [pdf]
1998
Ehrlich, S.M., Beck, D.M., Crowell, J.A., Freeman, T.C.A., & Banks, M.S. (1998). Depth information and perceived self-motion during simulated gaze rotations. Vision Research, 38, 3129-3146. [pdf]
Freeman, T.C.A., & Banks, M.S (1998). Perceived head-centric speed is affected by both extra-retinal and retinal errors. Vision Research, 38, 941-945. [pdf]
1997
Georgeson, M.A., & Freeman, T.C.A. (1997) Perceived location of bars and edges in 1-D images: Computational models and Human Vision. Vision Research, 37, 127-142. [pdf]
1996
Freeman, T.C.A., Harris, M.G., & Meese, T.S. (1996). On the relationship between deformation and perceived surface slant. Vision Research, 36, 317-322. [pdf]
Georgeson, M.A., Freeman, T.C.A., & Scott-Samuel, N.E. (1996). Sub-pixel accuracy: psychophysical validation of an algorithm for fine positioning and movement of dots on visual displays. Vision Research, 36, 605-612. [pdf]
1995
Meese, T.S., & Freeman, T.C.A. (1995) Edge computation in human vision: an orientation effect for two-component plaids. Perception, 24, 603-622. [pdf]
Meese, T.S., Harris, M.G., & Freeman, T.C.A. (1995). Speed gradients and the perception of surface slant: analysis is two dimensional not one dimensional. Vision Research, 35, 2879-2888. [pdf]
1994
Freeman, T.C.A., Harris, M.G., & Tyler, P.A. (1994). Human sensitivity to temporal proximity: the role of spatial and temporal speed gradients. Perception and Psychophysics, 55, 689-699. [pdf]
1992
Freeman, T.C.A., & Harris, M.G. (1992). Human sensitivity to expanding and rotating motion: effects of complementary masking and directional structure. Vision Research, 32, 81-87. [pdf]
Harris, M.G., Freeman, T.C.A., & Hughes, J. (1992). Retinal speed gradients and the perception of surface slant.Vision Research, 32, 587-590. [pdf]
Humphreys, G.W., Freeman, T.C.A., & Muller, H.M. (1992). Lesioning a connectionist model of visual search: selective effects on distracter grouping. Canadian Journal of Psychology, 46, 417-460.
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Research
Research Topics and Related Papers
1. Combining prior expectations and uncertainty to explain motion illusions during pursuit.
Pursuit adds motion to the image – movement on the retina doesn’t ‘line-up’ with the motion of objects in the world. The visual brain must therefore add estimates of eye velocity to estimates of image motion recover the motion of objects. 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 moving objects is distorted (trajectory misperception [4]) and self-motion veers away from its true path (e.g. the slalom illusion [5]). 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. We found that the speed of pursued stimuli was more difficult to discriminate than fixated stimuli. This suggests that observers are less certain about motion signals encoding eye speed. We used this result to quantify the Aubert-Fleischl phenomenon based on the assumption that our prior expectations for motion in the word is centred on zero. The account we developed highlighted an important property overlooked by current Bayesian models of motion perception. Two Bayes estimates are needed at a relatively early stage in the processing chain, one for eye velocity and one for image motion.
See Freeman, T.C.A., Champion, R.A., & Warren, P.A. (in press). A Bayesian model of perceived head-centred velocity during smooth pursuit eye movement. Current Biology.
2. 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
3. Do we have direct access to image motion during pursuit?
Pursuit adds motion to the image – movement on the retina doesn’t ‘line-up’ with the motion of objects in the world. The visual brain must therefore add estimates of eye velocity to estimates of image motion recover the motion of objects. Is this process mandatory? Put another way, do observers have any access to image motion before it is integrated with estimates of eye velocity? In this project we used speed discrimination to investigate the ‘direct-access’ hypothesis and discovered that observers were unable to base their discrimination judgements on image motion. This remained the case even when we gave them feedback on each trial based on the image motion 
their concurrent eye movement produced. We found that observers could not help but judge the relative motion between the pursued target and the background object. The use of relative motion was all conquering –when we removed the simultaneous relative motion, observers used the sequential relative motion between a previously seen pursuit target and the currently viewed background object.
See Freeman, T. C. A., Champion, R. A., Sumnall, J. H., & Snowden, R. J. (2009). Do we have direct access to retinal image motion during smooth pursuit eye movements? Journal of Vision, 9(1):33 [pdf].
Funded by the Wellcome Trust
Funding
BBSRC (2011-2014)
Studentship in collaboration with Dr Jon Erichsen, OPTOM
Royal Society International Travel Grant (2010)
£4000
“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”
ESRC: Project grant (2006)
£241,679
D.M. Jones, H.M. Hodgetts & T.C.A. Freeman
“Now, where was I? Cognitive models and support mechanisms for interrupted task performance.”
Wellcome Trust: Project grant (2002)
£184,257
T.C.A. Freeman
“The extra-retinal motion aftereffect”
EPSRC: Project grant (1999) £44,794
T.C.A. Freeman
“Perception of motion-defined depth during eye and head movements”
Wellcome Trust: Project grant (1999)
£102,612
T.C.A. Freeman & R.J. Snowden
“Human perception of head-centric motion”
Royal Society: Travel grant (1999)
£770
T.C.A. Freeman
Royal Society: Equipment grant (1998)
£9,100
T.C.A. Freeman
Research Group /internal collaborators
Simon Rushton (time-to-collision,; visual dominance)
Krish Singh (GABA and orientation discrimination project; brain imageing and active motion perception)
Suresh Muthukumaraswamy (GABA and orientation discrimination project)
Petroc Sumner (nystagmus, smooth pursuit and saccades)
Bob Snowden (motion sensitivity during pursuit)
Research Collaborators
David Alais (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
Tom Margrain (Cardiff Uni Optometry: Age, eye movement and motion sensitivity)
Postgraduate Students
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
Ben Dunkley (joint with Krish Singh). Ben has been investigating which regions of the brain are during active smooth pursuit eye movements, using both MEG and fMRI techniques. The aim is to delineate retinal and extra-retinal motion mechanisms and establish whether they encode speed or position. Another is to establish whether cortical extra-retinal activity depends specifically on those eye movements under our own volition.
James Harrison (joint with Petroc Sumner). James is investigating intentional saccadic eye movements during OKN and pursuit. He also plans to examine perceived location during OKN.
Previous Students
Alistair Barrowcliff (joint with Nicola Gray) – eye movement desensitisation and reprocessing
Rhys Davies - motion aftereffects and pursuit eye movement
Joni Karanka (joint with Simon Rushton) – time-to-collision
Jenny Naji – pursuit and motion-defined depth perception
Emer O’Connor - motion sensitivity and pursuit
Rhodri Woodhouse (joint with Simon Rushton) – eye dominance
Biography
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
Awards / External Committees
EPSRC peer-review college (2006-present day).
Editor, Perception
Employment
2008-present: 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