Robert F Hess

McGill University, Montréal, Quebec, Canada

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Publications (282)744.78 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, we investigate how the responses of the human visual pathway to temporal frequency are modified as information transfers between the lateral geniculate nucleus (LGN) and primary visual cortex (V1) and to the extrastriate areas of the dorsal and ventral streams (V2, V3, VP, V3A, V4, and MT). We use high-field fMRI (4 T) to record simultaneously the responses of these areas across temporal frequency for chromatic stimuli (L/M-cone opponent and S-cone opponent) and stimuli of high and low achromatic contrasts. We find that: (1) the LGN has relatively low-pass responses for temporal frequency at both high and low achromatic contrasts, indicating that LGN cell spiking activity is not well reflected in the BOLD response. In addition, M cell-like temporal responses were not found, even at low contrasts. (2) Responses in V1 and extrastriate areas V2, V3, VP, and V3A display a progressively low-pass dependence on temporal frequency for achromatic stimuli (2-16 Hz) and are flat for chromatic stimuli (2-8 Hz), showing little overall difference between chromatic and achromatic cortical temporal filtering. (3) Strongly differential effects are found between dorsal and ventral stream processing by the level of MT and V4. V4 shows a significant low-pass temporal dependence for all achromatic and chromatic stimuli, whereas MT has temporally high-pass or flat responses for achromatic and chromatic stimuli. MT was the only visual area that showed M cell-like responses. We conclude that the dorsal and ventral pathways of human vision progressively develop characteristic differences in temporal processing that affect both chromatic and achromatic stimuli.
    Journal of Vision 11/2010; 10(13):13. · 2.48 Impact Factor
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    ABSTRACT: We developed a binocular treatment for amblyopia based on antisuppression therapy. A novel procedure is outlined for measuring the extent to which the fixing eye suppresses the fellow amblyopic eye. We hypothesize that suppression renders a structurally binocular system, functionally monocular. We demonstrate using three strabismic amblyopes that information can be combined normally between their eyes under viewing conditions where suppression is reduced. Also, we show that prolonged periods of viewing (under the artificial conditions of stimuli of different contrast in each eye) during which information from the two eyes is combined leads to a strengthening of binocular vision in such cases and eventual combination of binocular information under natural viewing conditions (stimuli of the same contrast in each eye). Concomitant improvement in monocular acuity of the amblyopic eye occurs with this reduction in suppression and strengthening of binocular fusion. Furthermore, in each of the three cases, stereoscopic function is established. This provides the basis for a new treatment of amblyopia, one that is purely binocular and aimed at reducing suppression as a first step.
    Optometry and vision science: official publication of the American Academy of Optometry 09/2010; 87(9):697-704. · 1.53 Impact Factor
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    ABSTRACT: Although there is general agreement that the fMRI cortical response is reduced in humans with amblyopia, the deficit is subtle and has little correlation with threshold-based psychophysics. From a purely contrast sensitivity perspective, one would expect fMRI responses to be selectively reduced for stimuli of low contrasts. However, to date, all fMRI stimuli used in studies of amblyopia have been of high contrast. Furthermore, if the deficit is selective for low contrasts, one would expect it to reflect a selective M-cell loss, because M-cells have much higher contrast gain than P-cells and make a larger contribution to the threshold detection of stimuli of low spatial and medium temporal frequencies. To test these two predictions, we compared % BOLD response between the eyes of normals and amblyopes for low- and high-contrast stimuli using a phase-encoded design. The results suggest that the fMRI deficit in amblyopia depends upon stimulus contrast and that it is greater at high contrasts. This is consistent with a selective P-cell contrast deficit at a precortical or early cortical site.
    Human Brain Mapping 08/2010; 31(8):1233-48. · 6.88 Impact Factor
  • Source
    Richard Dallala, Yi-Zhong Wang, Robert F Hess
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    ABSTRACT: We extended a previous study (Hess et al. (1999). A deficit in strabismic amblyopia for global shape detection. Vision Research, 39, 901-914) where it was claimed that strabismic amblyopes exhibit a deficit for the detection of continuous radial frequency patterns, a task that is thought to involve global processing and in particular, a contribution of extra-striate area V4. We confirm this previous report using a novel Gabor-sampled stimulus and show that the deficit for the amblyopic eye occurs across a range of circular contour frequencies, that is the number of radial cycles per circular contour length in degrees. By arranging the Gabor-samples to coincide with either the peaks/troughs or zero-crossings of the radial modulation, we were able to tease apart the relative contributions of local position and local orientation respectively to the shape processing deficit. The deficit for the amblyopic eye involves both anomalous position and orientation coding with the latter being more affected than the former. While this suggests that ventral extra-striate processing is anomalous, it leaves open the possibility that the striate input may be responsible.
    Vision research 07/2010; 50(16):1612-7. · 2.29 Impact Factor
  • Source
    Andrew Isaac Meso, Robert F Hess
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    ABSTRACT: We investigated sensitivity to motion gradients psychophysically using a band-pass filtered white noise stimulus with two superimposed components moving in opposite directions and spatially modulated with out of phase periodic functions. An optimum sensitivity ratio of the carrier to the modulator frequency of about 11 was measured. Tuning for speed was also observed, with sensitivity falling off at higher speeds in a trend showing scale invariance, consistent with temporal frequency tuning. Similar tuning properties were observed for both luminance and motion contrast thresholds. These findings are consistent with local and global processes in striate and extra-striate cortex respectively and suggest the scale of second stage low frequency integration is broad and matched to the spatiotemporal scale of the sensitivity of first stage local filters. The finding of scale invariance over a large range in stimulus size of 4.6-37 degrees of visual angle suggest a general property of integrating neural mechanisms, which was identified here because of the use of narrowband stimuli.
    Vision research 05/2010; 50(15):1475-85. · 2.29 Impact Factor
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    ABSTRACT: Amblyopia or lazy eye is the most common cause of uniocular blindness in adults and is caused by a disruption to normal visual development as a consequence of unmatched inputs from the two eyes in early life, arising from a turned eye (strabismus), unequal refractive error (anisometropia), or form deprivation (e.g., cataract). Using high-field functional magnetic resonance imaging in a group of human adults with amblyopia, we previously demonstrated that reduced responses are observable at a thalamic level, that of the lateral geniculate nucleus (LGN). Here we investigate the selectivity of this deficit by using chromatic and achromatic stimuli that are designed to bias stimulation to one or other of the three ascending pathways (the parvocellular, magnocellular, and koniocellular). We find the greatest LGN deficit is for stimuli modulated along the chromatic, L/M cone opponent axis of color space, suggesting a selective loss of parvocellular function in the LGN. We also demonstrate a cortical deficit that involves all the visual areas studied (V1, V2, V3, VP, V3A, V4), and we find this is greatest for the two chromatic responses (S cone opponent and L/M cone opponent) versus the achromatic response, as might be expected from a loss of segregation of chromatic pathways in the cortex.
    Journal of Neurophysiology 05/2010; 104(1):475-83. · 3.30 Impact Factor
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    ABSTRACT: Much of the debate surrounding the precise functional role of brain mechanisms implicated in the processing of human faces can be explained when considering that studies into early-stage neural representations of the spatial arrangement of facial features are potentially contaminated by "higher-level" cognitive attributes associated with human faces. One way to bypass such attributes would be to employ ambiguous stimuli that are not biased toward any particular object class and analyze neural activity in response to those stimuli in a manner similar to traditional reverse correlation for mapping visual receptive fields. Accordingly, we sought to derive whole face representations directly from neural activity in the human brain using electroencephalography (EEG). We presented ambiguous fractal noise stimuli to human participants and asked them to rate each stimulus along a "face not present" to "face present" continuum while simultaneously recording EEGs. All EEGs were subjected to a time-frequency analysis near 170 ms (negative amplitudes near 170 ms post-stimulus onset have been linked to early face processing) for five different frequency bands (delta, theta, alpha, beta, and gamma) on a trial-by-trial basis, independent of the behavioral responses. Images containing apparent face-like structure were obtained for theta through gamma frequency bands for strong negative amplitudes near 170 ms post-stimulus onset. The presence of the face-like structure in the spatial images derived from brain signals was objectively verified using both Fourier methods and trained neural networks. The results support the use of a modified reverse correlation technique with EEG as a non-biased assessment of brain processes involved in the complex integration of spatial information into objects such as human faces.
    NeuroImage 02/2010; 51(1):373-90. · 6.25 Impact Factor
  • Source
    R F Hess, B Mansouri, B Thompson
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    ABSTRACT: The present treatments for amblyopia are predominantly monocular aiming to improve the vision in the amblyopic eye through either patching of the fellow fixing eye or visual training of the amblyopic eye. This approach is problematic, not least of which because it rarely results in establishment of binocular function. Recently it has shown that amblyopes possess binocular cortical mechanisms for both threshold and suprathreshold stimuli. We outline a novel procedure for measuring the extent to which the fixing eye suppresses the fellow amblyopic eye, rendering what is a structurally binocular system, functionally monocular. Here we show that prolonged periods of viewing (under the artificial conditions of stimuli of different contrast in each eye) during which information from the two eyes is combined leads to a strengthening of binocular vision in strabismic amblyopes and eventual combination of binocular information under natural viewing conditions (stimuli of the same contrast in each eye). Concomitant improvement in monocular acuity of the amblyopic eye occurs with this reduction in suppression and strengthening of binocular fusion. Furthermore, in a majority of patients tested, stereoscopic function is established. This provides the basis for a new treatment of amblyopia, one that is purely binocular and aimed at reducing suppression as a first step.
    Restorative neurology and neuroscience 01/2010; 28(6):793-802. · 2.93 Impact Factor
  • Journal of Vision - J VISION. 01/2010; 2(7):223-223.
  • P. C. Huang, R. F. Hess, S. C. Dakin
    Journal of Vision - J VISION. 01/2010; 4(8):781-781.
  • P.-C. Huang, K. T. Mullen, R. F. Hess
    Journal of Vision - J VISION. 01/2010; 6(6):229-229.
  • Journal of Vision - J VISION. 01/2010; 7(9):393-393.
  • Journal of Vision - J VISION. 01/2010; 5(8):265-265.
  • K. A. May, R. F. Hess
    Journal of Vision - J VISION. 01/2010; 6(6):337-337.
  • Journal of Vision - J VISION. 01/2010; 3(9):456-456.
  • R. F Hess, T. Ledgeway
    Journal of Vision - J VISION. 01/2010; 3(9):787-787.
  • Journal of Vision - J VISION. 01/2010; 4(8):14-14.
  • B. Mansouri, H. A. Allen, R. F. Hess
    Journal of Vision - J VISION. 01/2010; 4(8):764-764.
  • P.-C. Huang, R. F. Hess
    Journal of Vision - J VISION. 01/2010; 7(9):250-250.
  • H. A Allen, R. F Hess, T. Ledgeway
    Journal of Vision - J VISION. 01/2010; 3(9):532-532.

Publication Stats

5k Citations
744.78 Total Impact Points

Institutions

  • 1992–2014
    • McGill University
      • Division of Ophthalmology
      Montréal, Quebec, Canada
  • 2010–2013
    • Sun Yat-Sen University
      • State Key Laboratory of Oncology
      Guangzhou, Guangdong Sheng, China
  • 2009–2013
    • University of Auckland
      • Department of Optometry and Vision Sciences
      Auckland, Auckland, New Zealand
  • 2006–2013
    • Queensland University of Technology
      • • Institute of Health and Biomedical Innovation
      • • School of Optometry and Vision Science
      Brisbane, Queensland, Australia
    • Université de Montréal
      Montréal, Quebec, Canada
  • 2012
    • National Cheng Kung University
      • Department of Psychology
      Tainan, Taiwan, Taiwan
  • 2008–2012
    • Colgate University
      • Department of Psychology
      Hamilton, NY, United States
  • 2011
    • University of Waterloo
      Waterloo, Ontario, Canada
    • University of Ulster
      • Intelligent Systems Research Centre
      Belfast, NIR, United Kingdom
    • The University of Tokyo
      • College of Art and Science & Graduate School of Arts and Sciences
      Tokyo, Tokyo-to, Japan
    • Massachusetts General Hospital
      • Athinoula A. Martinos Center for Biomedical Imaging
      Boston, MA, United States
  • 2004–2008
    • Aston University
      • • School of Life and Health Sciences
      • • Department of Optometry
      Birmingham, ENG, United Kingdom
    • University of Birmingham
      • School of Psychology
      Birmingham, ENG, United Kingdom
  • 2002–2006
    • University of Nottingham
      • School of Psychology
      Nottingham, ENG, United Kingdom
  • 2005
    • Retina Foundation of the Southwest
      Dallas, Texas, United States
    • Dalhousie University
      • Department of Psychology and Neuroscience
      Halifax, Nova Scotia, Canada
    • City University London
      • Division of Optometry and Visual Science
      London, ENG, United Kingdom
  • 1999–2003
    • University College London
      • Institute of Ophthalmology
      London, ENG, United Kingdom
    • University of Houston
      • College of Optometry
      Houston, TX, United States
    • University of Bradford
      Bradford, England, United Kingdom
  • 1997–2000
    • York University
      • • Centre for Vision Research
      • • Department of Psychology
      Toronto, Ontario, Canada
  • 1993–2000
    • Cornell University
      • Department of Psychology
      Ithaca, NY, United States
  • 1997–1999
    • University of California, Irvine
      • Department of Cognitive Sciences
      Irvine, CA, United States
  • 1996
    • Université du Québec à Montréal
      Montréal, Quebec, Canada
  • 1989–1992
    • University of Cambridge
      • Department of Psychology
      Cambridge, ENG, United Kingdom