In a nutshell: Identifying an object in an unexpected location is quick, but responding to it is slowed down.

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The visual world is complex, but much of what we encounter every day is predictable. For example, at a café, we know that our coffee order will be placed on top of the counter, rather than under a table, and the small paper packets beside it are more likely to contain sugar than salt. This prior knowledge helps us to identify objects in predictable circumstances more quickly than things we see in an unfamiliar or inconsistent context.

Prior knowledge is acquired without effort or intent through our daily interactions with the world. However, how and when the brain uses this knowledge as it processes visual information is not well understood.

Brain Function CoE Chief Investigator Jason Mattingley and Associate Investigator Paul Dux, along with postdoctoral researcher Michelle Hall from the University of Queensland, recorded brain activity in a group of people while they viewed mandala-like assortments of shapes on a computer screen.

The shapes were more likely to appear in certain locations. For example, the purple mandala almost always appeared at the top right of the screen, but occasionally a different mandala would appear there instead. Over time, participants developed an expectation of where each mandala would appear, but they were never explicitly told the precise pattern. Each mandala was mapped to a key on the keyboard, and participants were asked to indicate which shape was on the screen at each point in time by pressing the relevant key as quickly as possible.

Participants were slower to respond – and had different brain activity – when the mandala appeared in an infrequent location on the screen. Unlike previous studies, which suggested that prior knowledge is integrated with sensory input at the earliest stage of visual processing, the researchers found that this difference in brain activity arose at the middle stages of visual processing. This means that identifying the shape of an object is not affected by whether or not it matches our prior knowledge, but choosing the correct response is.

Next steps:
The team continues to investigate how the brain uses prior knowledge when processing visual information. They are using brain imaging techniques to record patterns of brain activity while participants view surprising and unsurprising shapes.

Hall, M. G., Mattingley, J. B., & Dux, P. E. (2018). Electrophysiological correlates of incidentally learned expectations in human vision. Journal of Neurophysiology, doi: 10.1152/jn.00733.2017

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