CAPLAB

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Address

William Guild Building, Room S7
University of Aberdeen
Kings College
Old Aberdeen
AB24 3FX
The United Kingdom

Research

A crucial question in vision science is how do we recognize objects? It seems trivial, easy, and self-evident, but taking a cursory look at today's artificial intelligence research (or at face detection software in cameras) is enough to suggest how incredibly complex the process is. At our lab, we have been working on uncovering the mechanisms underlying object recognition, using visual crowding as a tool. Currently, we are working on determining the neural processes underlying attention, object recognition and visual short term memory (VSTM) using a combination of psychophysics and EEG.

Object recognition

Object recognition takes place in two steps. First, the features (orientation, color, etc) of an object are detected independently. Then these features are put together to form the representation of that object. Crowding is a breakdown of the second step. When a target object is flanked closely by other objects, the features of the target and the flankersget mixed up leading to a jumbled percept. This is crowding. It offers a direct window into how feature integration occurs, and hence serves as a handy tool in investigating object recognition.

Crowding is illustrated below. Fixate (keep your eyes focused) on the black square in the center. If you try to read the central letter of the triplet on the right, you will find it very hard. The same letter at the same distance on the left is extremely easy to identify. It is the presence of the the flanking letters on the right that makes the target letter unidentifiable.

Crowding demo

Attention

Visual attention directs the limited resources of the visual system to the currently relevant input. We are interested in how attention is deployed in space in order to select objects. Currently, We are applying a variety of techniques including Steady State Visual Evoked Potentials, Multivariate Classifiers and Representational Similarity Analysis to EEG data obtained in attentional tasks to determine the shifts in spatial attention as a function of time. Similar techniques are also being applied to determine how the brain represents various features of objects, such as location and motion.

Current Research

  • Neural oscillations in attention, awareness and VSTM
  • Neural basis of crowding
  • Subitization
  • Time perception

People

Current Members

  • Rama's Pic

    Rama Chakravarthi

    Lecturer

  • Rama Chakravarthi

    Lecturer and PI

  • Leili's Pic

    Leili Soo

    Doctoral student

  • Leili Soo

    Doctoral student

  • Oana's Pic

    Oana Iosif

    Doctoral student

  • Oana Iosif

    Doctoral student

  • Kyle's Pic

    Kyle Ferris

    MRes student

  • Kyle Ferris

    MRes student

Former Postgraduate Members

  • Josephine's Pic

    Josephine Reuther

    Doctoral student

  • Josephine Reuther

    PhD

  • Nick's Pic

    Nicholas Hall

    MRes

  • Nicholas Hall

    Doctoral student

Former Undergraduate Members

  • Sid's Pic

    Sid Henriksen

    Honours student

  • Sindre Henriksen

    Honours student

  • Diana's Pic

    Diana-Maria Marosi

    Honours student

  • Diana-Maria Marosi

    Honours student

  • Robert's Pic

    Robert Ainsley

    Summer intern

  • Robert Ainsley

    Summer intern

    Robert's summer internship was supported by the Developing Scientisits fund, during the summer of 2014. He worked on whether visual crowding could be alleviated by priming.

    Robert is a tennis enthusiast and runs his own tennis training service. He recently graduated from the University of Aberdeen.

Publications*

  • § Reuther, J. and Chakravarthi, R. (2017). Does self-prioritization affect perceptual processes?, Visual Cognition, 1 - 18. abstract pdf doi
  • Jennings, B. J., Tsattalios, K., Chakravarthi, R., and Martinovic, J. (2016). Combining S-cone and luminance signals adversely affects discrimination of objects within backgrounds, Scientific Reports, 6 (20504): 1-10. abstract pdf doi
  • Costa, S. L., Gonçalves, O. F., DeLuca, J. Chiaravalloti, N., Chakravarthi, R., and Almeida, J. (2015). The temporal dynamics of visual processing in Multiple Sclerosis, Applied Neuropsychology: Adult, 23 (2): 133 - 140. abstract pdf doi
  • Rosen, S., Chakravarthi, R., and Pelli, D. G. (2014). The Bouma law of crowding, revised: Critical spacing is equal across parts, not objects, Journal of Vision, 14 (6): 10, 1-15. abstract pdf Covered in a blog. doi
  • Chakravarthi, R., Carlson, T. A., Chaffin, J., Turret, J., and VanRullen, R. (2014). The temporal evolution of coarse location coding of objects: Evidence for feedback. Journal of Cognitive Neuroscience, 26 (10): 2370 - 2384. abstract pdf doi
  • Reuther, J. and Chakravarthi, R. (2014). Categorical membership modulates crowding: evidence from characters, Journal of Vision, 14 (6): 5, 1-13. abstract pdf doi
  • Van Vugt, M. K., Chakravarthi, R., and Lachaux, J. P. (2014). For whom the bell tolls: periodic reactivation of sensory cortex in the gamma band as a substrate of visual working memory maintenance, Frontiers in Human Neuroscience, 8: 696. abstract pdf doi
  • Chakravarthi, R. and VanRullen, R. (2012). Conscious updating is a rhythmic process, Proceedings of the National Academy of Sciences, 109 (26): 10599-10604. abstract pdf doi
  • Freeman, J.,Chakravarthi, R., and Pelli, D. G. (2012). Substitution and pooling in crowding, Attention, Perception, & Psychophysics, 72 (4): 379 - 396 abstract pdf doi
  • Chakravarthi, R. and Pelli, D. G. (2011). The same binding in contour integration and crowding, Journal of Vision, 11 (8): 10, 1-12. abstract pdf doi
  • Chakravarthi, R. and VanRullen, R. (2011). Bullet trains and steam engines: Exogenous attention zips but endogenous attention chugs along, Journal of Vision, 11 (4):12, 1-12. abstract pdf doi
  • Chakravarthi, R. and Cavanagh, P. (2009). Recovery of a crowded object by masking the distracters: Determining the locus of feature integration, Journal of Vision, 9 (10):4, 1-9. abstract pdf doi
  • Chakravarthi, R. and Cavanagh, P. (2009). Bilateral field advantage in visual crowding, Vision Research, 49 (13): 1638 – 1646. abstract pdf doi
  • Vickery, T. J., Shim, W. M., Chakravarthi, R., Jiang, Y. V., and Luedeman, R. (2009). Supercrowding: Weakly masking a target expands the range of crowding, Journal of Vision, 9 (2):12, 1-15. abstract pdf doi
  • Chakravarthi, R. and Cavanagh, P. (2007). Temporal properties of the polarity advantage effect in crowding, Journal of Vision, 7 (11): 1 – 12. abstract pdf doi
  • Ramakrishna, C. (2002). Real latencies and facilitation, Consciousness and Cognition, 11(2): 300 – 303. pdf doi

Manuscripts in progress

  • Poncet, M., Chakravarthi, R., and Fabre-Thorpe, M (Submitted). Interactions between visual categories can be explained by overlap of neural activity.
  • Reuther, J. and Chakravarthi, R. (in preparation). Higher level crowding: Is it all just experimental design?

Conference presentations

  • Leili, S., Chakravarthi, R., and Andersen, S. A. (2015). The effects of contrast dissimilarity on crowding. Talk presented at the 14th annual meeting of the Scottish Vision Group, Scotland, UK.
  • Reuther, J. and Chakravarthi, R. (2015). Category effect in visual crowding = feature differences + overlap differences. Talk presented at the 14th annual meeting of the Scottish Vision Group, Scotland, UK.
  • Reuther, J. and Chakravarthi, R. (2014). Evidence for categorical crowding. Talk presented at the 13th annual meeting of the Scottish Vision Group, Scotland, UK.
  • Marosi, D-M. and Chakravarthi, R. (2014). Losing track of time: Time perception in cooperation and competition. Talk presented at the British Psychological Society Scottish Branch UG conference at Edinburgh, UK.
  • Poncet, M., Chakravarthi, R., and Fabre-Thorpe, M. (2014). The clash of visual categories. Poster presented at the 14th annual meeting of Vision Sciences Society, St Petersburg, FL.
  • Chakravarthi, R. and VanRullen, R. (2012). Evidence for the Lisman model of short-term memory: Modulation of theta-gamma coupling by the number of items in memory. Poster presented at the annual meeting of the Society for Neuroscience, New Orleans, USA.
  • Chakravarthi, R., Carlson, T. A., Chaffin, J., Turret, J. and VanRullen, R. (2011). O brother, where art thou? Locations of 1st and 2nd order objects are represented in the same way but at different times, as revealed by single-trial decoding of EEG signals. Talk presented at the European Conference on Vision and Perception, Toulouse, France.
  • Chakravarthi, R. and VanRullen, R. (2011). Attention is a state of mind: Phase of ongoing EEG oscillations predicts the timing of attentional deployment. Poster presented at the 11th annual meeting of Vision Sciences Society, Naples, FL.
  • Rosen, S., Chakravarthi, R., and Pelli, D. G. (2010). Crowding is grouping. Talk presented at the 11th annual meeting of Vision Sciences Society, Naples, FL.
  • Rosen, S., Chakravarthi, R., and Pelli, D. G. (2010). Grouping is fundamental to object recognition. Talk presented at the European Conference on Vision and Perception, Lausanne, Switzerland.
  • Chakravarthi, R. (2010). Mechanisms in crowding and blink: what can they tell us about consciousness? Symposium chaired at the 14th annual meeting of Association for the Scientific Study of Consciousness, Toronto, Canada.
  • Chakravarthi, R. and Rosen, S. (2010). Pool party: Admit one. Talk presented at the 14th annual meeting of Association for the Scientific Study of Consciousness, Toronto, Canada.
  • Chakravarthi, R. and VanRullen, R. (2010). Beam me up Scotty! Exogenous attention teleports but endogenous attention takes the shuttle. Talk presented at the 10th annual meeting of Vision Sciences Society, Naples, FL.
  • Pelli, D. G., Freeman, J., and Chakravarthi, R. (2010). Crowding combines. Talk presented at the 10th annual meeting of Vision Sciences Society, Naples, FL.
  • Rosen, S., Chakravarthi, R., and Pelli, D. G. (2010). Pool party, objects rule! Poster presented at the 10th annual meeting of Vision Sciences Society, Naples, FL.
  • Granata, Y., Chakravarthi, R., Rosen, S., and Pelli. D. G. (2010). Size pooling. Poster presented at the 10th annual meeting of Vision Sciences Society, Naples, FL.
  • Chakravarthi, R., Tillman, K., and Pelli, D. G. (2009). Features used or features available? Talk presented at the 9th annual meeting of Vision Sciences Society, Naples, FL.
  • Veenemans, A., Cavanagh, P., and Chakravarthi, R. (2009). Crowding by invisible flankers. Poster presented at the 9th annual meeting of Vision Sciences Society, Naples, FL.
  • Chakravarthi, R. and Pelli, D. G. (2008). What role does contour integration play in crowding? Talk presented at the 8th annual meeting of Vision Sciences Society, Naples, FL.
  • Rosen, S., Chakravarthi, R., and Pelli, D. G. (2008). Nasotemporal asymmetry in crowding. Talk presented at the 8th annual meeting of Vision Sciences Society, Naples, FL.
  • Vickery, T. J., Shim, W. M., Jiang, Y. V., Chakravarthi, R., and Luedeman, R. (2008). Supercrowding: Weakly masking a target greatly enhances crowding. Talk presented at the 8th annual meeting of Vision Sciences Society, Naples, FL.
  • Chatterjee, G. and Chakravarthi, R. (2008). Characterization of flickering-flanker induced blindness phenomenon. Poster presented at ECVP 2008, Utrecht, Netherlands.
  • Chakravarthi R., Rajagopal, A.K., and Usha Devi, A. R. (2008). Quantum mechanical basis of vision. Talk presented at India-US workshop on Science and Technology at the Nano-Bio Interface, Bhubaneshawar, India.
  • Chakravarthi, R. and Cavanagh, P. (2007). The effect of distracters on enumeration in the periphery. Poster presented at the 7th annual meeting of Vision Sciences Society, Sarasota, FL.
  • Chakravarthi, R. and Cavanagh, P. (2006). Hemifield independence in visual crowding. Talk presented at the 6th annual meeting of Vision Sciences Society, Sarasota, FL.
  • Chakravarthi, R. and Cavanagh, P. (2005). Temporal properties of the polarity advantage effect in crowding. Poster presented at the 5th annual meeting of Vision Sciences Society, Sarasota, FL.

§ Preregistered/Presubmitted Study

* Copyright notice: The publishers of these articles hold the copyright. The pdf version of the articles has been provided for download only as a means to ensure timely dissemination of scholarly and technical work. You may not distribute them, make them available for download by others, or use them for any profit-making enterprise. The articles may not be re-posted without the explicit permission of the copyright holder

Rama's CV

You can download a pdf of my CV here.

Education and Employment

2012 – Present: Lecturer, School of Psychology
University of Aberdeen, Scotland UK
2009 – 2012: Post Doctoral Fellow; Advisor: Dr. Rufin VanRullen
Centre de Recherche Cerveau et Cognition CNRS, Toulouse, France,
2007 – 2009: Post Doctoral Fellow in Psychology and Neural Science; Advisor: Prof. Denis Pelli
New York University, New York NY
2002 – 2007: PhD in Psychology: Cognition, Brain and Behavior; Advisor: Prof. Patrick Cavanagh
Harvard University, Cambridge MA
1999 – 2001: M.S. in Consciousness Studies; Advisor: Dr Shantanu Nagarkatti
Birla Institute of Technology and Science, Pilani, India
1993 – 1999: M.B., B.S. (Bachelor of Medicine, Bachelor of Surgery)
Manipal Academy of Higher Education, Manipal, India

Grants and Funding

2014 – : Exploring the neural basis of visual crowding, Eastbio BBSRC Doctoral Training Programme awarded to Ms. Leili Soo, ~£92,000
2014 – : Neural correlates of Blindsight, Elphinstone PhD Scholarship awarded to Mr Nicholas Hall, ~£15,000
2013 – : Mechanisms of Visual Crowding, Anderson Postgraduate (PhD) Scholarship awarded to Ms Josephine Reuther, ~£50,000
2014: Developing Scientists Summer Placement awarded to Mr. Robert Ainsley Henriksen, £1000
2012: Developing Scientists Summer Placement awarded to Mr. Sindre Henriksen, £1000
2006 – 2007: Graduate Society Dissertation Completion Fellowship, Harvard University, $18,000
2007: Stimson travel grant for presenting at VSS conference, 2007, $500
2006: McMasters travel grant for presenting at VSS conference, 2006, $500
2005: Graduate Society Fellowship Summer Award, Harvard University, $3,000
2004: Mind, Brain and Behavior Graduate Student Award, Harvard University, $5,000
2003 – 2004: Harvard University Graduate Summer Awards, $3,000/year
2002 – 2004: Harvard University GSAS Merit Fellowship, $70,000
2000 – 2001: Sir Ratan Tata Trust Scholarship for the M.S. Program, INR 15,000

Teaching Experience

Current responsibilities

Level 1:
  1. Introductory Psychology II: Evolutionary Psychology module
  2. Introduction to Biological Sciences: Consciousness module
Level 2:
  1. Advanced Psychology A: Methods and Applications - Methods in vision and attention
  2. Perception
Level 3: Methodology B: Semester long research projects (5-6 students each semester)
Level 4:
  1. Senior honours (research-based) thesis (4 students each year)
  2. Behavioural science thesis (1-2 students each year)
  3. Sixth Century Course on Consciousness (Levels 3 and 4)
Masters: Professional research skills I: Web design and maintenance in academia
Others:
  1. Level 3 Memory and Language Tutorials
  2. Level 4 Critical Review

Past Responsibilities

2003 – 2005: Teaching Fellow, The Evolution of Human Nature. Taught by Professors Marc Hauser and Richard Wrangham, Harvard University, 2 semesters
2004 – 2006: Teaching Fellow, The Human Mind. Taught by Professor Steven Pinker, Harvard University, 2 semesters

Research Supervision

PhD:
  1. Josephine Reuther (2013-present)
  2. Nicholas Hall (2014-present)
  3. Leili Soo (2014-present)
Masters:
  1. Samuel Pitt (2013-2014)
  2. Mentored 3-month internships at CerCo, CNRS, France (2010-2011):
  • Julie Chaffin
  • Marion Baziard
  • Alexy Assaf

Admin Responsibilities

  • Level 3 Methods B Course Coordinator
  • Member of Ethics Committee
  • Equality and Diversity Committee
  • Psychology Webpage maintenance
  • Social media outreach
  • Organising Perception and Attention group meetings

Professional Affiliations

  • Society for Neuroscience
  • Vision Sciences Society
  • European Conference on Visual Perception
  • Scottish Vision Group
  • Karnataka Medical Council, India

Reviewer

  • Attention, Perception, and Psychophysics
  • Journal of Cognitive Neuroscience
  • Journal of Experimental Psychology: Human Perception and Performance
  • Journal of Vision
  • Vision Research
  • NeuroImage
  • Frontiers in Psychology
  • Review Editor: Frontiers of Consciousness Research

Invited Talks

2014: The role of neural oscillations in visual processing. Presented at the University of Bangor, Wales
2013: When one's company, two's a crowd in object recognition. Presented at Workshop on crowding, EPFL, Lausanne, Switzerland.
2012: One rule to bind them all. Presented at the British Science Festival, Aberdeen UK
2011:
  1. Object recognition: Tales from crowding, updating and decoding. Presented at CerCo, CNRS, Toulouse.
  2. Object recognition. Presented at the School of Psychology, University of Aberdeen, Scotland, UK.
  3. When one's company, two's a crowd in object recognition. Presented at CerCo day symposium, Camaran, France.
2010: Object recognition and visual attention. Presented at the Center for Brain and Cognitive Sciences, University of Allahabad, India.
2007:
  1. The role of attention in crowding. Presented at the Visual Attention lab, Harvard Medical School and Brigham and Women's hospital, Boston.
  2. The role of attention in crowding. Presented at the Department of Psychology, New York Univeristy, New York.
  3. Mechanisms in Visual Crowding. Presented at the Cognition, Brain and Behavior Research Seminar, Harvard University.
2006: The Resolution of Visual Consciousness. Presented at Mind, Brain, and Behavior Graduate Seminar Series, Harvard University.