Judging the timing of sight and sound: differences between older and younger adults

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).

 

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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 allisonm@unimelb.edu.au

New publication: People with visual snow perceive luminance and contrast differently from controls

 

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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 allisonm@unimelb.edu.au

Balloon party! Celebrating theses submissions

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.

cassie submission

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.

nikki submission

Congratulations to our balloon-holding students!

Farewell to Fumi

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!

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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

New publication: Centre-surround visual processing of contrast: ageing affects mechanisms that operate within eyes but not between eyes

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.

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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.

New paper: ageing effects on peripheral vision

We have recently published the first paper from Menaka’s PhD, investigating how healthy ageing affects the perception of visual stimuli in the presence of surrounding features in peripheral vision. In particular, we are interested in the area of our field of view that is just outside of the centre (the fovea), which we refer to as the parafoveal area. Studying parafoveal vision is important in older adults, especially as foveal damage occurs in age-related conditions like macular degeneration, which may lead to increased reliance on parafoveal vision.

One aspect of vision that occurs in the parafovea is crowding, which is typically described as reduced object recognition in a cluttered scene. Another visual phenomenon that occurs in the parafovea is surround suppression. An example of suppression occurs when a person’s ability to detect that a visual target is present is worse when there are surrounding features. We measured crowding and surround suppression effects in 20 older and 21 younger adults. Observers focused on the centre of a computer screen and visual stimuli were presented in their peripheral vision (8 degrees from where they were fixating). Examples of what were presented are shown in the figure below.

menaka-stimuli

Top: To measure the effect of crowding, we presented a target (right, striped pattern) next to an extra piece of clutter known as a flanker (left, cross hatched pattern) Bottom: To measure the effect of surround suppression, the target (right, centre striped pattern) is presented with or without a surrounding half annulus. The white dot is the fixation spot for both tasks.

We found that older adults have reduced ability to detect a visual target when it was surrounded (more surround suppression) compared to the younger observers, but crowding was unaffected by the type of stimuli used in our study. This suggests that crowding and surround suppression may be distinct visual phenomena, despite both occurring in parafoveal vision.

An extra question we asked was: given previous reports of decreased visual attention with healthy ageing, could altered performance on the crowding and surround suppression tasks be explained by changes to visual attention? Our specific measure of attention was a visual search task. Indeed, our group of older adults showed decreased visual attention but neither crowding nor surround suppression showed a relationship to the attentional aspect.

Advancing our knowledge on the ageing effects on peripheral visual function is useful for future remediation strategies using peripheral vision in older individuals where foveal vision is hindered. The article can be viewed online here.

2016: It’s a wrap!

2016 has again been a busy year for our lab. Key highlights from our research areas of interest:

  1. 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.
  2. 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.
  3. 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.

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Above: Chongyue He (Honours student) graduated in December 2016

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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).

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Above: Our end-of-year event was held at the Brunswick Bowling Club in mid December with barefoot bowls and a bbq dinner