Q.State the determinants of selective attention. How does selective attention differ from sustained attention?

Attention has been classified in several different ways, but one especially useful, process-oriented view divides it into two broad types: selective attention and sustained attention. Selective attention is chiefly concerned with the problem of choosing a limited number of stimuli or objects for processing out of a much larger set of stimuli competing for notice, because our perceptual system has only a limited capacity to receive and process information at any given moment. Which particular stimuli actually get selected depends on both external factors (properties of the stimuli themselves, such as their size, intensity, movement, novelty, moderate complexity, and suddenness -- large, bright, moving, sudden, or intense stimuli tend to capture attention more easily) and internal factors within the perceiver (motivational factors linked to biological or social needs, such as a hungry person noticing even a faint smell of food; and cognitive factors such as personal interest, attitude, and 'preparatory set,' a kind of mental readiness that predisposes someone to respond to one type of stimulus rather than another). Psychologists have proposed several theories to explain exactly how this selection happens. Broadbent's filter theory proposes that many stimuli enter our receptors at once, creating a kind of 'bottleneck,' and that after passing briefly through short-term memory, a selective filter allows only a single stimulus through for higher-level processing at any one moment, while the remaining stimuli are screened out entirely at that point in time. Treisman's filter-attenuation theory modifies this by proposing that stimuli which do not get through the filter are not fully blocked but merely weakened (attenuated) -- which explains why a highly personally relevant stimulus, such as hearing one's own name spoken quietly across a noisy room, can still occasionally slip through and be noticed. Johnston and Heinz's multimode theory treats attention as an even more flexible system that can select a stimulus for processing at any of three different stages -- a sensory-representation stage, a semantic (meaning-based) representation stage, or a stage where both sensory and semantic representations enter awareness -- with selection at the earlier stage requiring less mental effort than selection at a later stage. Sustained attention, by contrast, is concerned less with selecting among stimuli and more with the ability to maintain concentration on a single object or event continuously over a long period of time; it is also called vigilance, and is essential in situations such as air-traffic control or radar monitoring, where signals appear unpredictably and even a brief lapse could be costly. So, in short, selective attention deals with choosing among many competing stimuli at a given instant, whereas sustained attention deals with holding concentration on one thing across an extended stretch of time; performance on sustained-attention tasks is, in turn, shaped by factors such as sensory modality, clarity, intensity/duration of the stimulus, and how predictable its timing and location are.