Our environment often contains visual and auditory information originating from separate events. Our brains need to be able to combine related sensory information coming from the same event and separate unrelated information from different events. One of the few common approaches to investigate such behaviour in human observers is known as audiovisual synchrony judgement: visual and auditory stimuli are presented at the same time or at some time offset from each other. Observers judge whether each stimulus pair is perceived as occurring at the same time (synchronous) or at different times (asynchronous). Previous work in our lab has shown that older adults are more likely to perceive asynchronous pairs as synchronous – i.e. older adults are more likely to incorrectly combine unrelated sensory information. How then does this reflect in the underlying brain processes involved in multisensory combination?
In this newly published study, we evaluated the impact of healthy ageing on the brain processes underlying audiovisual synchrony judgement using electroencephalography (EEG). EEG is used to measure brain activity in response to a stimulus (in this case, visual and auditory information). In the particular task used in this study, older and younger adults performed the same perceptually, but older adults recruited more widespread brain areas (specifically fronto-polar and frontal regions) to maintain the similar level of performance (see Figure 1 below).
Figure 1: EEG activity indicating more widespread brain areas recruited by the older adults (bottom panel) to perform the audiovisual synchrony judgement task for synchronous pairs as compared to younger adults (top panel). A similar finding was also found for asynchronous audiovisual pairs (see published paper for details). Figure adapted from Figures 3 and 4 of Chan, Pianta, Bode & McKendrick (2017).
This work has been published in the journal Neurobiology of Aging (click here to view the abstract). A full copy of the paper can be requested by contacting Allison at email@example.com
Visual snow is a rare neurological condition where people see static-like ‘snow’ (continuous tiny dots similar to the noise of an analogue TV) in their vision all of the time. Other common complaints are seeing afterimages and excessive floaters and experiencing tinnitus. The precise cause of visual snow is not understood, however, symptoms are thought to be due to excessive neural firing in the visual areas of the brain (cortical hyperexcitability).
In this study, we tested patients with visual snow on four visual perceptual tasks that are believed to indirectly measure visual cortical hyperexcitability. Two of the tasks, luminance increment detection in spatial noise and centre surround contrast matching, were chosen as they test early stages of the visual processing. The other two tasks, global form perception and global motion discrimination, assess relatively later stages of the visual processing pathway.
We found that people with visual snow process luminance and contrast differently from controls, consistent with elevated excitation in the early stages of the visual processing pathway (higher luminance increment detection threshold and higher perceived contrast in the presence of a high contrast surround grating). This work reveals promise for the future development of visual tests that may help differentiate visual snow from other disorders and quantify the effectiveness of treatments.
The paper has been published in Neurology and was conducted in collaboration with Assoc Prof Owen White from Melbourne Health (Royal Melbourne Hospital); and Assoc Prof Joanne Fielding from Monash University. To access a full copy of the paper, please contact Allison directly at firstname.lastname@example.org
The tradition at the University of Melbourne is to receive a well-earned balloon once you have submitted your thesis. Our lab celebrated two theses submissions recently:
1) Cassie Brooks submitted her MPhil thesis on 28th April 2017. One paper has been published describing work from her thesis in Journal of Vision, which can be accessed in full here.
2) On 13th May 2017, Nikki Rubinstein submitted her PhD thesis “Incorporating spatial information into visual field testing algorithms”. To date, Nikki has successfully published one paper from her PhD work in Translational Vision Science and Technology, which you can read at this link.
Congratulations to our balloon-holding students!
This week we said farewell to Dr Fumi Tanabe, who is an ophthalmologist from Osaka, Japan. Fumi visited our lab for approximately 1.5 years with a special interest in glaucoma, and worked on a number of research projects using the high resolution optical imaging device in our laboratory (optical coherence tomography). She will be missed!
Fumi (middle, bottom) and her farewell cake with ‘fluorescein green’ topping, pictured with members of our laboratory and other staff and students at the Department of Optometry and Vision Sciences, University of Melbourne
As described in our previous lab blog posts, we have a long standing interest in trying to understand how healthy aging affects vision. Specifically, many of our research projects involve the design of experiments that can tell us more about which visual neural processes are altered by the aging process. A number of our experiments have investigated a phenomenon called centre surround contrast suppression. This phenomenon describes the visual experience in which a high contrast grey and white pattern will appear to be of lower contrast when surrounded by another higher contrast pattern. By manipulating different aspects of the central or surround pattern, we can test separate neural pathways that are responsible for visual experience.
In this particular experiment, we take advantage of the anatomical fact that neurons that carry information from the two eyes do not directly communicate until they reach the areas of the brain responsible for visual processing.
Centre surround contrast suppression can be elicited when by showing the centre and surround pattern to the same eye (‘within eye’ suppression). This is how most studies are conducted. Centre surround contrast suppression can also be elicited by showing the centre pattern to one eye and the surround pattern to the other eye (‘between eyes’ suppression). ‘Between eyes’ suppression is particularly informative because we know that it can only occur once information from the two eyes is combined in the brain. In this study, we measured both ‘within eye’ and ‘between eyes’ suppression. The figure below shows the visual patterns used in the study and summarises the results.
When the centre and surround patterns were shown to both eyes, the amount of suppression (i.e. the amount by which the contrast of the centre pattern appeared lower than its actual contrast) was higher in older individuals than in younger individuals. However, when the centre and surround patterns were shown to different eyes, both younger and older individuals showed similar amounts of suppression. This indicates that the difference between older and younger adults is not general, but quite specific to the “within eye” condition.
The complete findings of this study have been recently published in Journal of Vision and can be accessed here.
2016 has again been a busy year for our lab. Key highlights from our research areas of interest:
- Glaucoma: A highlight of our program this year was a visiting PhD student, Clement Beugnet, from the University of Lille, France. Clement’s research is interested in how glaucoma impacts on complex visual processing of objects and scenes. 2016 also provided an opportunity for PhD candidate, Nikki Rubinstein, to present her work at an international conference (22nd International Perimetry and Imaging Symposium) in Udine, Italy. We also welcomed two additional postdoctoral researchers to the lab: Astrid Zeman and Phil Bedggood.
- Migraine: In 2016 we continued a large, 3 year study that will determine whether migraine events can be predicted by daily testing of vision on an portable tablet device (iPad), which has primarily been conducted by postdoctoral research fellow Janet Chan. We have also been involved in a collaborative project with the Royal Melbourne Hospital investigating a rare condition known as visual snow. Part of this work was presented this year at the international Asia Pacific Conference on Vision in Fremantle, Western Australia.
- Healthy ageing: In 2016, we welcomed two Honours students (Chongyue He and Huda Waraich) to the lab who conducted novel experiments looking at how healthy ageing impacts on the processing of moving objects. These types of experiments may have relevance to driving or other tasks where detecting moving objects is critical to performance. Both students have successfully completed their Honours year, so congratulations!
A recent highlight was Allison winning the ‘No-Bell Prize’ at the Melbourne Neuroscience Institute’s final event for the year in December. The competition requires researchers to communicate what they do to a wider audience without the use of jargon or technical words. Each time a scientific word is used that is not comprehensible, one of the judges can ring a bell. The least number of bells wins!
Thank you to all of our marvelous volunteers for assisting in our research program during 2016, and we wish you all the best for the festive season.
Above: Chongyue He (Honours student) graduated in December 2016
Above: Our research leader Allison brings home the ‘No-Bell Prize’ trophy for the Department of Optometry & Vision Sciences for the second year running (last year’s winner was Dr Christine Nguyen).
Above: Our end-of-year event was held at the Brunswick Bowling Club in mid December with barefoot bowls and a bbq dinner