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Visual Perception and Cognition

Understanding the Complexity of the Visual System

The human visual system uses approximately one third of its cortical processing power, yet we see the horizontal lines here as tilted, such is the difficulty of the task that confronts it. In order to understand how the visual system functions, we conduct research on a diverse range of topics, using the tools of Visual Psychophysics, Transcranial Magnetic Stimulation and Electrophysiology.

Areas of interest include:

  • Sound and Vision
  • Tracking Multiple Objects and Attention
  • Texture Perception
  • Spatial Localization and Acuity
  • Vision in Noise
  • Visual Illusions
  • Motion Perception
  • Peripheral Vision and Scaling

Tracking Multiple Objects

How good are we at attending to several items at the same time? In this project, our 'items' are dots moving in straight lines through a gap. One of the dots changes direction. How easy is it to detect this, and does the task get harder with more dots? These experiments help us understand how attentional and memory resources are distributed when monitoring several items.

What Kinds of Correlations can we See?

Jigsaw puzzles work because missing parts of the puzzle look similar to their surroundings; that is, they are positively correlated with their neighbours. But how good are we at this guessing game in general? Subjects looked at images where the centre tile was removed, and had to guess what luminance it was. Nearby tiles were correlated with each other in different ways. Subjects were good at guessing in the left image, where all correlations are positive. Prediction is difficult in the right image, because nearby tiles are opposites. These experiments show that we cannot perceive negative correlations, which are rare in nature.

Interactions Between The Senses

In the experiment shown here, a sound influences when (or at what location) an observer sees a moving dot reverse its direction. Real-world events involve both sound and vision, but how do we integrate the information from our eyes and ears into a single unified percept? We are interested in the effects of sound on visual perception, and vice-versa.

We also study somatosensory (tactile) stimuli as a third modality, with particular interest in the relative perceived timing of events across the modalities. It emerges that perceived time is far more flexible than previously thought, being particularly susceptible to recent experience.
An additional area of interest is the way in which our motor actions relate to our sensory perception. In a particularly fascinating illusion, we are able to trick the brain into perceiving a sensory event prior to the motor action producing the event!

The Central Performance Drop

Almost all visual tasks are easiest when located at the position where we are looking. An exception may be texture pop-out. In the image shown here, subjects who are looking at the centre of the image are best at detecting a small 3x3 texture region when it is 6° away from the line of sight.

Investigating this phenomenon helps us understand how the visual system processes textured images at different retinal eccentricities. The drop in pop-out detection at fixation may be related to the change in the size of the most easily detected texture patch with eccentricity.

Funding

Our research is funded by the EPSRC, BBSRC, the Leverhulme Trust, the College of Optometrists, the Royal Society, charities, and the Wellcome Trust. We also undertake contract research and consultancy work.

Investigators