Dr. Bernhard Ross

Research Focus

Publications

Research Projects

1. Binaural processing in young and older adults

Aging related changes in the central nervous system result in functional deficits such as processing of temporal sound structures and processing of binaural information. Consequently, speech communication especially in noisy environment might be severely impaired in elderly persons even when their aided thresholds are normal. Behavioural tests often fail to distinguish between central auditory processing disorders and attention deficits. Therefore, objective tests for central auditory function are essential. We shall employ a new dichotic stimulus paradigm eliciting robust cortical responses specific for binaural processing of inter-aural time differences. With whole head magnetoencephalography we shall record responses to tone onsets and change in binaural timing as well 40-Hz steady-state responses simultaneously from two groups of 20 young and 20 older adults. Comparison with behavioural tests will give new insights in age related changes of central auditory processing and test the proposed method as a diagnostic tool.
The project is funded by the Hearing Foundation of Canada

• Human auditory 40-Hz steady-state responses
  

Auditory steady state-responses (ASSR) are oscillatory brain responses at the frequency of stimulation. The sources of MEG recorded are mainly in primary auditory cortex and may be a part of the thalamo-cortical network. We investigated the temporal dynamics of ASSR evoked with amplitude modulated sounds. A main working hypothesis is that the ASSR are related to temporal processing of auditory information.

• Right hemispheric laterality of 40-Hz ASSR
  

A common observation with whole head MEG recording of the ASSR was that the amplitudes in the right auditory cortex were larger than in the left. We compared laterality of auditory evoked responses (P1, N1, sustained response, transient gamma band response) with the laterality of the ASSR. Common to all auditory evoked responses is the effect of larger responses in the hemisphere contra-lateral to the stimulated ear, however, the sustained response and more pronounced the ASSR showed right hemispheric dominance. We discussed the observed effect as evidence for right hemispheric processing of the stimulus periodicity.

• Stimulus induced reset of 40-Hz ASSR
  

ASSR to amplitude modulated sound are strongly affected by a concurrent stimulus even if this distracting stimulus is presented to the contra-lateral ear and is spectrally distinct from the ASSR generating sound. The time-course of amplitude and phase of the induced change in the ASSR resembles that of the ASSR onset. Our hypothesis is that the onset like response after distraction indicates a reset of oscillatory activity. The results are discussed as an example for a reset mechanism in oscillatory networks.

• Does selective attention modulate the ASSR
  

Induced and evoked oscillatory activity in the gamma frequency-band (30-80 Hz) are discussed being related to binding of sensory information.Moreover, evidences exist that gamma-band activity is involved in attentional processes. That posed the question, whether the 40-Hz ASSR might be modulated by attention. We compared 40 Hz ASSR to amplitude modulated sound under attention to the auditory stimulus with those during attention focused to a visual task. Whereas significant ASSR enhancement 300-400 ms after stimulus onset in the attended condition was found, it seems that the 40-Hz ASSR is only little affected by changes in attention.

2. Oscillatory activity related to memory load in a working memory task

(Collaboration with Jeremy Caplan, Rotman Research)

3. Brain responses to music: effects of long-term musical training

(Collaboration with Takako Fujioka, Rotman Research and Laurel Trainor, McMaster University, Hamilton)

4. Multi-sensory interaction in the auditory and visual system

(Collaboration with Anthony Herdman, Rotman Research)

5. Segregation and persistence of form in visual perception

(PI: Susanne Ferber, University of Toronto)

6. Laterality of frontal alpha activity and emotions

(Collaboration with Cheryl Grady, Rotman Research and Wil Cunningham, University of Toronto)

Research Funding

2008-2011   Neural mechanisms of auditory-based remediation programs, Investigators: Claude Alain, Bernhard Ross, and Kelly Tremblay, Sponsors: Canadian Institutes for Health Research (CIHR), 85,000$ per annum for 3 years

2007-2010   Characterizing fMRI and MEG signals in the somatosensory cortex, Investigtors, Simon Graham, Wilkin Chau, Randy McIntosh, Bernhard Ross, Jon Ween, Sponsors: Canadian Institutes for Health Research (CIHR), 100,000$ per annum for 3 years

2007   Magnetoencephalography as a possible diagnostic tool for traumatic brain injury: Cortical oscillations during retrieval from working memory, Investigator:  Bernhard Ross, Sponsor: Dept. for Medicine University of Toronto, The Deans Fund, 10,000$ one year

2007    Auditory cortex activation indicating audiovisual integration during listening and reading, Investigators Bernhard Ross and Hao Luo, Sponsors: The Hearing Foundation of Canada, 24,500 $ for one year 

2007-2012    Improved characterization of human somatosensory cortex using simultaneous vibro-tactile stimulation Investigators: Bernhard Ross; Sponsors: Natural Sciences and Engineering Research Council of Canada (NSERC),  26,000$ per annum vor five years

2006-2011    Aging related changes in central hearing - A neuromagnetic study Investigators: Bernhard Ross; Terence Picton, Claude Alain Sponsors: Canadian Institutes for Health Research (CIHR), 136,000$ per annum for five years

2006-2008    Transformation of whole head magnetoencephalographic data onto standardized sensor position Investigators: Bernhard Ross; Wilkin Chau Sponsors: Natural Sciences and Engineering Research Council of Canada (NSERC), 45,000$ per annum for three years

2005-2005    Binaural Processing in young and older adults Investigators: Bernhard Ross; Sponsors: The Hearing Foundation of Canada, 23,500 $ for one year

Contact

The Rotman Research Institute
Baycrest
3560 Bathurst Street, 1032
Toronto, Ontario,
Canada M6A 2E1

Phone: 416 785 2500 x2690
Fax: 416 785 2862
Email: brossrotman-baycrest.on.ca