ABSTRACT
This chapter explores the various top-down factors that can affect sensory perception and explore the cognitive mechanisms that play key roles in that process. The roles of various other high-level cognitive factors, such as motivation, emotion and culture are then taken up in the context of guiding the perceptual set. The phenomena that have been discussed thus far have led a group of psychologists and cognitive scientists to make a forceful case for a constructivist theory of perception, which stresses the role of knowledge and other cognitive operations in perception. The emergence of experimental psychology in the 19th century began an era of intense research on attention. The reach of attention covers all sensory systems, though the visual and auditory systems are the most affected and therefore have been studied in far greater detail. The earliest studies of attentional modulation on neural activity were undertaken with awake, behaving monkeys and largely on neurons in higher visual areas of the brain.
