Vision relies on attention to the environment

By Prof. Zijiang He
Department of Psychological & Brain Sciences

We can easily appreciate that attention is required to perform daily activities, such as reading, learning, driving and playing sports. Indeed, the topic of attention is one of the most studied across multiple scientific disciplines including the disciplines of cognitive science, neuroscience, perception, artificial intelligence, learning and development.  Despite this, it remained unknown whether attention plays a critical role in constructing the vast visual perceptual space, which acts as an internal 3-D schema within which object localization, cognitive operations, space orientation, and motor planning occurs. 

Debunking conventional wisdom, Prof. Zijiang He (Psychological & Brain Sciences) and a team of researchers report, in "Attention modulates perception of visual space" published in the December 2016 edition of Nature Human Behaviour, that our visual system relies on attention control to obtain reliable visual space. 

We all know that our visual space is rich in appearance and reliably guides our interactions in the physical world. At issue, is whether the appreciation of visual space requires attention control? The conventional wisdom is that attention plays little or no role at all. This is because of our everyday experience of effortlessly perceiving a vivid volume of space in front of us immediately upon opening our eyes. Such ease of perceiving visual space is in contrast to the effort required to scrutinize an object in the environment. Indeed, current visual and cognitive neuroscience theories assume that the visual system automatically creates the vast visual space, and only then is attention used to bind simple features of objects and to orient to sensory events within the visual space.

Prof. He and his team found that an ambient attention mechanism in the environmentselects the ground surface (our terrestrial niche) to use as bases and scaffolds to form the vast visual world. In the study, observers stood in the dark while directing their attention to either the upper or lower visual field. A textured surface, either delineating the ground or ceiling was then displayed, and followed by a briefly presented target. We found that perceived target location was more accurate only when both the textured surface was on the ground and the observers directed attention to the lower visual field. Attending to the upper visual field with textured ceiling or ground surface, or in total darkness, led to less accurate location judgment. This indicates that visual space is more accurately formed when the twin-factor of ambient attention to the lower field and having a visible ground surface are met.

Effectively, this finding also provides an explanation as to why humans are efficient in perceiving visual space in our everyday-lighted environment. This is because upon opening our eyes, our brain automatically directs attention to the ground surface so that the visual system can quickly construct an internal representation of the ground surface, from which visual space is established. This means that our brain has an ambient attention mechanism that is well adapted to our particular ecological niche (ground surface).

For humans and other terrestrial creatures, the ambient attention mechanism has a bias for the terrain below our feet (ground). This also makes sense because when we walk on the ground or drive on the road, we often use our ambient attention to cover a large area of the ground or a large stretch of the road. By extension, non-terrestrial animals (e.g., aquatic or arboreal) would exhibit different biases. If this prediction is confirmed, it would be fascinating to discover that amphibious animals such as penguins and seals have mechanisms with dual-biases to fit both niches (land and water).

Prof. Zijiang He (Psychological & Brain Sciences) and his team found that perceived target location was more accurate only when both the textured surface was on the ground and the observers directed attention to the lower visual field. An ambient attention mechanism in the environment selects the ground surface (our terrestrial niche) to use as bases and scaffolds to form the vast visual world.

Major points:

• Visual space is defined as the visual perceptual space that encompasses the observer and the objects the observer is viewing.

• Scientists who study “visual space” try to understand how we visually perceive the space between the observer and the objects the observer is observing.

• We previously showed that visual space in total darkness is represented by the intrinsic bias (visual system’s default), and the shape of the intrinsic bias below the eye level is different from the one above the eye level (Science Advances, 2016). In that paper, we showed that the intrinsic bias (visual space) of a taller person results in him/her being more accurate in judging object location than a shorter person.

• In the current Nature Human Behaviour paper, we asked a more fundamental question. That is, whether our perception of visual space is facilitated by allocating (paying) attention to it.  We found the answer in the affirmative.

• Our finding reveals that being able to allocate attention makes our perception of visual space superior. It makes us more accurate in judging object location. 

• But while attention is needed for us to perceive visual space, there is a catch. We found that attention’s role in facilitating visual space perception only occurs when two conditions are met. Specifically, attention must be allocated to the visual field below the eye level and the ground surface must be visible.

• The figures below show that when there is visible texture on the ground in an otherwise dark room, paying attention to the lower field (left figure) leads to more reliable visual perceptual space (yellow region) than to the upper field (right figure). The visual perceptual space is less compressed in the left figure, allowing it to encompass a larger volume of space, and hence, making object location judgments more accurate than a compressed visual space (right figure).

• Thus besides the attention finding per se, which is novel, our finding also provides additional evidence supporting the theory that the ground surface holds a special significance for us (as terrestrial creatures).