Our eyes relay a continuous stream of images to the brain. We are unaware of most of this input, because processing every detail would require resources that far exceed the available neural capacity. Attention is the mechanism by which the brain selects the most important features of the sensory streams. For example, we monitor the colour of a traffic light at a busy intersection. Although keeping track of the locations of important features feels effortless, in fact the image of the traffic light moves on the retina with each eye movement, while our gaze scans pedestrians and traffic. How to keep attention fixed on a stable location as the eyes move around is a difficult problem.
To solve this problem, the brain must integrate eye-centered representations with information about the rotation of the eyes in the orbits. The sources of the eye rotation information for spatial attention are currently unknown. One candidate signal is corollary discharge: a copy of the oculomotor command fed back into the visual system to provide a prediction of how information will shift on the retina as a consequence of the eye movement that is about to be executed (Cavanagh et al. 2010). A second candidate is oculoproprioception: input from the extraocular muscles providing information about the eye’s movement and position in orbit (Odoj and Balslev 2016). It is difficult to manipulate oculomotor and oculosensory signals in healthy humans to study their role in perception and behaviour, so not much is currently known about their relative roles in supporting stable attention.
Recent methodological breakthroughs allow us to now address this question using transcranial magnetic stimulation (TMS). We will use TMS over the somatosensory cortex to alter the oculoproprioceptive signal and induce the illusion of eye rotation (Balslev and Miall 2008). Then, using visual psychophysics, we will attempt to detect a corresponding shift in visual attention by the same angular displacement. Likewise, oculomotor signals will be manipulated with TMS over the frontal eye fields to determine the impact on attention. These experiments will identify the ocular signals that are incorporated into the brain’s attention maps. Characterizing the sensorimotor building blocks in human attention representations can help us understand attention disorders (e.g. spatial neglect) and, in the future, contribute to the design of more efficient rehabilitation strategies (e.g. by manipulating these signals with transcranial magnetic stimulation).
To carry out this project, the student will benefit from the joint supervision of a cognitive neuroscientist (Dr Daniela Balslev), whose pioneering research in the human oculoproprioceptive system prompted the research question, and a psychologist (Dr Amelia Hunt), who has a strong background in the study of the coupling between eye movement and spatial attention. The student will have access to state-of-the-art laboratories at the Universities of St Andrews and Aberdeen.
Balslev D, Miall RC. 2008. Eye position representation in human anterior parietal cortex. J Neurosci. 28:8968–8972.
Cavanagh P, Hunt AR, Afraz A, Rolfs M. 2010. Visual stability based on remapping of attention pointers. Trends Cogn Sci. 14:147–153.
Odoj B, Balslev D. 2016. Role of Oculoproprioception in Coding the Locus of Attention. J Cogn Neurosci. 28:517–528.