Our senses process a massive amount of information, yet the world around us seems quite straightforward. Selective attention and expectations play an important role in this. ‘What we see every day and every moment is actively constructed by our brain. This is shaped by the knowledge we already have about the world, which gives rise to expectations about what we may see in our sensory environment, and also by attention, guided by what we find relevant,’ says neuroscientist Josipa Alilović. She examined this impact of attention and expectations on perception, recording brain processes down to the millisecond. She will defend her PhD thesis at the University of Amsterdam on Friday, 2 July.
As you walk through the busy streets of Amsterdam, your attention can easily jump back and forth between the person you are walking with, the beautiful historic façades of the canal-side homes and the approaching cars you anticipate on the left. We see the world around us seemingly effortlessly, yet we are constantly shaping our reality. We usually don’t think about this remarkable ability of our brain to produce conscious perception and thoughts.
Neuroscientist Josipa Alilović shines a spotlight on the brain’s capacity for conscious perception. She shows how our selective attention and expectations about the sensory environment influence what we perceive in the world around us. ‘We think we see the world as it really is, but this isn’t true. What we see every day and every moment is actively constructed in our brain. This is shaped by the knowledge we already have about the world and what we find relevant at a given moment,’ Alilović explains.
This illusion clearly shows how our expectations can determine what we see. The hollow mask rotates, but we are unable to see its reverse (concave) side. We are used to seeing faces from the front, so our brain keeps filling in this convex image for us.
Alilović examined the earliest point at which our perception is affected by attention and expectations. When do attention and expectations begin to impact the sensory visual information we receive? Using EEG recordings of brain activity, she was able to capture brain processes with millisecond precision which could then be read out using the-so-called decoding approach. ‘This method of multivariate pattern analysis has been referred to as the first step towards mind-reading.’ Alilović says.
While test subjects were completing visual tasks on a computer, EEG recordings were made which were then used to decode and track in time various stages of visual information processing, leading to perception and awareness. ‘We were really able to peek into the brain and decode what the brain was representing, before the participants consciously saw it themselves. This allowed us to capture the role of attention and expectations in the process of perception.’
Just a few hundreds of milliseconds after the test subject had seen an image, attention and expectations already started to affect the process. Alilović says that while this is remarkably early, it was, however, found that initial visual response in the brain may be impenetrable to influences by attention and expectation.
Alilović also examined what happens when we report perceiving something different than what was shown to the eye. In one of the studies, test subjects were shown an image of a face or an image of a house. Recording the brain processes showed that when people reported the wrong image (i.e., a house instead of a face), their brain already relayed incorrect information before the test subject was aware of it, after which the test subject also consciously perceived this incorrect image. ‘Incorrect expectations on the part of the brain can therefore lead to incorrect conscious perception, which underscores the powerful impact of this process,’ Alilović says.
Alilović’s research reveals the impact that selective attention and predictions have on our visual perception. ‘Perception isn’t just determined by the light that hits your retina,’ she says. ‘Perception is actively constructed and significantly shaped by our attention and expectations. This challenges the classical idea of perception.’
These findings advance our understanding of the complex neural processes that shape our conscious perception of the world.
Josipa Alilovíc, ‘Seeing beyond vision. Understanding how attention and prediction shape conscious visual perception.’ Supervisors: Prof. H. A. Slagter and Prof. S. van Gaal
Friday 2 July, 16:00, Agnietenkapel Amsterdam. The ceremony will also be made available to watch via a live stream.