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Hierarchical Visual Processing

Models of hierarchical processing with simple cells feeding into complex cells.

While the eye is a complex structure, it is just the start of an even more complex series of processing stages for visual information in the brain. People might be surprised to here that around 40% of the human brain is involved in one way or another with visual processing: humans are very visual animals. Once signals leave the eye they enter the brain via the thalamus, which organizes the inputs from the two eyes.

Once this has occurred the signals are sent to the primary visual cortex at the rear of the head. We usually refer to this brain area as visual area one, or V1.

The processing that occurs in V1 is complex and it has taken 50 years to uncover those basic properties, starting with the Nobel Prize winning work of Hubel and Wiesel at Harvard Medical School and continued in no small part by the critical contributions made by Australian scientists.

Professor Peter Bishop is regarded as the Australian founding father of this Australian research interest and the National Vision Research Institute is proud to continue that focus.

Spatiotemporal tuning of cortical cells at high and low contrast. Tuning is contrast dependent, suggesting alterations to the hierarchical flow of information.

The areas of the brain that process visual information are divided into distinct compartments, each with its own map of visual space. V1 is the first cortical area and around 30 more visual areas have been identified. In some cases information is passed serially from one area to the next, e.g. V1 to V2.

However, many of the connections break these strict hierarchical rules and non-hierarchical interconnections between visual brain areas are the norm rather than the exception. All this interconnectivity offers the brain an amazing richness of processing capacity but also makes it very challenging to establish how the brain does that processing.

At the NVRI we investigate the pathways within V1 and V2 to understand how information is transformed between these steps. Our findings have shown that each processing step leads to a more complex signal that is informed by the input from the outside world and the influence of higher level processing in the brain.

Ultimately, what we see is determined not just by what is in the visual scene but also by what we want to find in the visual world.

These questions are of a basic science nature but inform future medical discoveries by uncovering some of the mysteries associated with the visual system.