Visual processing

There is a traditional view that visual processing follows a feedforward system where there is a one-way process by which light is sent from the retina to higher cortical areas, however, there is increasing evidence that visual pathways operate bidirectionally, with both feedforward and feedback mechanisms in place that transmit information to and from lower and higher cortical areas.

[1] Various studies have demonstrated this idea that visual processing relies on both feedforward and feedback systems (Jensen et al., 2015; Layher et al., 2014; Lee, 2002).

Studies with monkeys have also shown that neurons in higher level visual areas are selective to certain stimuli.

These deficits are caused by damage to brain structure implicated in either the ventral or dorsal visual stream (Barton 2011).

It does however appear that the PPA is associated with visual processing of buildings and places, as patients who have experienced damage to the parahippocampal area demonstrate topographic disorientation, in other words, unable to navigate familiar and unfamiliar surroundings (Habib & Sirigu, 1987).

Similar to the PPA, the FFA exhibits higher neural activation when visually processing faces more so than places or buildings (Kanwisher et al., 1997).

However, the fusiform area also shows activation for other stimuli and can be trained to specialize in the visual processing of objects of expertise.

Other experiments have studied the ability to develop expertise in the FFA using 'greebles', a visual stimulus generated to have a few components that can be combined to make a series of different configurations, much like how a variety of slightly different facial features can be used to construct a unique face.

This suggests that the FFA and PPA may have developed certain specializations due to the common visual tasks within those fields of view.