Links between attention and eye movements
Credit: Special Arrangement
Bengaluru: The links between attention and eye movements and the processes through which the brain coordinates the two are the focus of two new studies from the Centre for Neuroscience (CNS), Indian Institute of Science (IISc).
Attention allows us to focus on a specific object and ignore distractions as we look at it. It is understood as tightly coupled with rapid eye movements, called saccades, prompting many studies on pre-saccadic attention – a phenomenon where even before our eyes move towards an object, attention focuses on it, allowing us a clearer perception.
In a study, CNS researchers show that this perceptual advantage is lost when the object changes suddenly, a split second before our gaze falls upon it, making it harder for us to process what changed. Devarajan Sridharan, Associate Professor at CNS and corresponding author, said the study – published in PLOS Biology – provided an “interesting counterpoint” to previous studies which suggested that pre-saccadic attention is always beneficial.
Priyanka Gupta, a PhD student in Sridharan's lab, trained human volunteers to covertly monitor gratings (line patterns) on a screen, without directly looking at them, and to report when one tilted slightly. She noted that participants did this just before their eyes moved, in the pre-saccadic window. A tracker of eye-movements before, during and after their gaze fell on the object revealed that the participants found it harder to detect the changes in the pre-saccadic window.
IISc said a follow-up experiment also established the loss of this pre-saccadic attentional advantage. Sridharan said such insights could be useful in tracking multiple objects in rapidly changing environments, like driving or flight simulators.
Tracking monkeys’ gaze
In another study carried out with collaborators at Stanford University, the researchers used an unusual experiment to decouple attention from eye movements in monkeys. The monkeys had been trained on a counter-intuitive, “anti-saccade” task; they covertly monitored several gratings on a computer screen without directly looking at them. But when any one grating tilted slightly, the monkeys had to look away from it instead of focusing more on it. This helped the researchers delink the location of the monkey’s attention, from the location where its gaze ultimately fell. The study was published in Science Advances.
Electrodes recorded signals from hundreds of neurons across layers of the visual cortex area V4 in the monkey’s brain. Neurons in the more superficial layers generated attention signals, while neurons in deeper layers produced eye movement signals; both types showed different activity patterns.
Adithya Narayan Chandrasekaran, the first author of the study and a former research assistant in Sridharan’s lab, said the superficial neurons increased their firing rates, to signal the object that needs to be attended to and prioritised for decision-making. The deep neurons, meanwhile, were tuning down their “noise”, possibly to allow the animal to perceive the object better.
Sridharan said discovering such mechanisms was vital for developing therapies for disorders like ADHD.