Award details

Perceptual learning of shapes in the human visual cortex

Reference	BB/D52199X/1
Principal Investigator / Supervisor	Professor Zoe Kourtzi
Co-Investigators / Co-Supervisors
Institution	University of Birmingham
Department	School of Psychology
Funding type	Research
Value (£)	301,400
Status	Completed
Type	Research Grant
Start date	05/12/2005
End date	04/06/2009
Duration	42 months

Abstract

The detection and recognition of visual objects is a vital skill for our interactions in the world. To achieve it, the brain has to group local image features into global perceptual units (objects). This process of perceptual integration is a challenging operation for the visual system as objects are often camouflaged in the cluttered environments we inhabit. The extent of the difficulty of this problem is highlighted by the fact that perceptual integration processes develop slowly (between 5 and 14 years of age) and are severely disrupted by visual deficits early in life. Recent behavioural studies have shown that learning can be a key facilitator in perceptual integration for the detection and recognition of objects in cluttered scenes. Further, neurophysiological studies suggest that learning enhances the sensitivity of neural processing. However, little is known about the role of learning in shaping perceptual integration and visual recognition processes across stages of visual analysis in the human brain. The aim of the proposed research is to use human psychophysics and brain imaging to provide significant new insight into the neural plasticity mechanisms that support behavioural improvement in perceptual integration and visual recognition. In particular, we will use concurrent psychophysical and fMRI methods to measure behavioural responses and bold signals across visual areas (early retinotopic and higher occipitotemporal) before, and after, training in a shape discrimination task. We will use stimuli resembling the camouflage conditions in natural images, namely a target object¿s contours will be defined by local elements that have similar orientation and are co-aligned along a curved path. To achieve different degrees of camouflage by the surrounding elements, these contour paths will be embedded in different types of backgrounds. Our three studies will address the following questions: (1) How does the human visual brain learn objects in natural clutteredscenes? We will investigate learning-based plasticity at different cortical stages of visual analysis for shapes embedded in noisy backgrounds. (2) Does the human visual brain take advantage of natural image regularities (e.g. grouping of elements with similar orientation) that determine the distinctiveness of targets when learning novel objects in cluttered scenes? We will compare learning for low salience shapes embedded in noisy backgrounds and high salience pop-out targets embedded in uniform texture backgrounds. (3) Does learning facilitate perceptual integration and shape detection in the absence of regularities that usually mediate grouping of shape contours in natural images? We will test learning-based plasticity for unnatural contours that are defined by co-oriented but not co-aligned elements. (4) What is the nature of the shape representations (i.e. training-specific vs abstract) formed during learning? We will investigate transfer of learning across changes in the position and orientation of the trained shapes. (5) Are different types of adaptive processing mediated by similar plasticity mechanisms? We will compare the effects of learning via training and priming via repeated stimulus exposure. This work will provide (a) significant insights into the role of learning in shaping brain functions that mediate key perceptual and cognitive abilities, and (b) the foundation for studying the role of learning in visual or cognitive deficits that impair these functions.

Summary

Every time you board an aeroplane the airport security staff x-ray your bags to check that they don¿t contain dangerous items. This job is not easy, dangerous objects are often hard to spot because they are camouflaged by surrounding objects that have a similar appearance. Working out what is inside your bag from the x-ray requires that the operator decides which bits of the x-ray image go together to make up meaningful objects. This challenging task is actually something that our brains do whenever we open our eyes. Somehow, despite the clutter of the world around us, our brains put together all the pieces of the visual image so that we can quickly identify interesting target objects and work out what to do with them. This is a critical skill for survival: from identifying predators or prey and recognising poisonous foods, to diagnosing tumours on medical images and finding familiar faces in the crowd. Unfortunately, our brains don¿t always get it right and we can miss important objects in the world. How does the brain respond to this problem and improve our performance? An intuitive answer comes from the compelling observation that practice makes perfect. Training improves our ability to detect and identify targets in cluttered natural scenes. However, we do not yet fully understand how the brain mechanisms that support this learning work. Our research project aims to improve our understanding of how our brains learn to recognise target objects in the cluttered visual environments we inhabit. We will use advanced brain scanning technology to examine how brain activity changes in different areas of the brain when we are trained on the difficult task of detecting and identifying objects in cluttered scenes. We will investigate the effects of learning on our ability to (a) group together pieces of a scene (e.g. a tiger moving behind trees), (b) identify objects with distinctive features that pop out in a scene (e.g. a tall man in the crowd) or even (c) detect unfamiliar objects that are hidden by surrounding structures (e.g. objects on x-rays). Changes in brain activity after training in these tasks will provide evidence that learning modifies brain functions important for the detection and recognition of novel objects in complex environments. Investigating these problems not only improves our understanding of our own brain, but also helps us to understand what goes wrong when people suffer brain damage so that we can design training techniques to help them recover from their impaired abilities.

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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