Every moment of their lives, organisms from pigeons to people are bombarded by a wide array of visual stimuli. Some of these stimuli are relevant to current circumstances and goals, whereas others are not. How does the visual system distinguish relevant from irrelevant stimuli?
One adaptive strategy may be to establish which visual regions are figures and which are backgrounds. Figures correspond to objects that should be attended to, recognized, and acted upon, whereas backgrounds correspond to the spaces between objects, and should be ignored.
We have developed a behavioral task in which pigeons were trained to discriminate whether a target spot appeared on a colored figural shape or on a differently colored background (Lazareva, Castro, Vecera, & Wasserman, 2006). Using this task, we found that the birds were faster to detect the target, to report its location, and to learn the correct response on figure trials than on background trials. We also found that this figural benefit is more pronounced when the figural region was smaller (Castro, Lazareva, Vecera, & Wasserman, 2010).
We are also exploring neurobiological underpinnings of figure-ground segregation in collaboration with Martin Acerbo (Iowa State University). Our current working hypothesis is that the avian midbrain nucleus called nucleus rotundus is most likely to be involved in figure-ground assignment. The inhibitory input to nucleus rotundus is provided by nucleus subpretectalis / isthmi-pretecto-subpretectalis (SP/IPS); thus, SP/IPS is also likely to play a critical role in figure-ground segregation.
We have shown that both nucleus rotundus and SP/IPS are more active after figure-ground discrimination task than after other, control tasks confirming our hypothesis that these two structures may be critically involved in figure-ground assignment (Acerbo et al., 2012). In addition, bilateral chemical lesions of SP/IPS significantly impaired figure-ground discrimination but not shape discrimination or color discrimination (Scully, Acerbo, & Lazareva, 2014). Finally, we found that intracranial administrations of bicuculline and muscimol into the SP/IPS had a detrimental effect on birds' performance further confirming that inhibitory input from this nucleus is essential for successful figure-ground discrimination (Acerbo & Lazareva, submitted).
We are currently exploring metabolic activity associated with figure-ground discrimination in entopallium (a higher-level visual nucleus) and in nucleus isthmi (a regulatory center for deep layers of optic tectum). This work will help us establish potential involvement of other brain areas located either upstream or downstream from nucleus accumbens.
Comparative Perception and Attention Laboratory