Ch 6 Key Concepts Flashcards
Top down process
In top down processing we use stored (learned )knowledge to interpret sensory information. This can be contrasted with bottom up processing which uses information from the senses. Gregory’s constructivist theory of perception emphasises the importance of top-down process, by suggesting that we form perceptual hypotheses by combining incomplete sensory data with stored knowledge to determine what is being perceived. He supports his theory with visual illusions, such as the Müller-Lyre figure, suggesting that it is interpreted in terms of learned knowledge of the world; we look at the figure as being a corner, with the line which appears to be longer being perceived as further away, and adjusted through size constancy, Segall et al support this from tests of the Bete people, who live in a jungle environment lacking corners and therefore show little susceptibility to the illusion. Conversely, the illusion can be explained by what is present in the stimulus, e.g. Day
suggests we make a perceptual compromise between the actual line length and the overall object of which it is a part. While the importance of top-down processing is challenged by Gibson’s theory of direct perception, Gregory’s theory is valuable as it integrates top-down and bottom up processing, highlighting the use of both. However it doesn’t provide a complete picture of perception and overestimates the role of top-down processing therein underestimating the richness of sensory information.
Limited capacity attention
As he brain is limited in the amount of information it can process, Kahneman suggested that the limited capacity central processor is responsible for integrating incoming info with stored memory. He proposed that the higher level of stimulation, more info can be processed, therefore ignoring other irrelevant details (this implies a interference). Posner & Boies dual-task studies support the theory, in which they found that participants responded more slowly (i.e. with either right or left hand) to a letter and auditory tone presented simultaneously rather than one after the other. However McLeod replicated the study, but with two different responses (speaking and hand gesture) in which response times were not slowed, suggesting that humans have different pools of resources, thereby indicating that we are not drawing on a limited capacity central processor. This has led to multiple-resource theories of attention. However, it is difficult to establish how such pools are divided and resources allocated. There may also be a single higher pool to integrate lower level processing; Kahneman and multiple resource theories could be looking at different levels of the system, not different systems. Kahneman’s idea of limited capacity attention is important, due to an awareness of our processing limitations as well as encouraging further research and theories about how our brains process information.
Attentional spotlight
As we cannot process all info in visual field, Posner suggests that the attentional spotlight (metaphor) describes how it filters information to highlight a small area, thereby giving this info priority for processing. Erikson & Murphy propose that attention works like a zoom lens; when focused tightly in one area, attention is ‘zoomed in’ when broadened it’s ‘zoomed out’. This principal applies to how we listen to music, by focusing on one instrument (spotlight zoomed in) and a piece of musical played by several instruments (spotlight zoomed out). The theory of attentional spotlight is valuable as it suggests that we control what we process ie attention is selective which involves cognitive processes such as expectancy. However, Lavie suggested that perceptual load may affect the size of the spotlight; for example when driving attentional tunnelling occurs as load is high, anything outside region likely to receive no processing. Yet also some evidence to suggest we do not have control of over where the spotlight is directed referred to as stimulus-induced shifts of attention, which is driven by the environment. This could be influenced by endogenous system processes such as motivation or external factors which are part of exogenous system processes.
Bottleneck theory of Attention
Broadbent suggests that a bottleneck in the attentional system allows a small amount of sensory info that is filtered on the basis of physical characteristics and offers that this operates early in the system, so that most incoming info receives no conscious processing. In a split span experiment Broadbent presented 3 digits simultaneously to each ear and participants were asked to report the digits in pairs or from one ear then the other. He discovered that the participants found it easier to recall from one ear then the other whereas the pairs condition was more difficult. According to this, it implies that meaning is not processed, yet Treisman found that attention switches to unattended info if it is meaningful. This indicates that there is some semantic processing of unattended info, which is highlighted in the ‘cocktail party effect’ - where if in conversation with someone, attention is switched if we hear our own name in an unattended conversation. Deutsch & Deutsch challenge bottleneck theories, and suggest there are no resource limitations on processing; selection takes place at the response stage. Whether selection is early or late appears to depend on the situation. Lavie’s experiment clarifies this by demonstrating that if perceptual load is high the filter operates early and if the load is low it operates later.
Gibson’s direct perception
Gibson suggests that all that is needed for perception is provided by sensory information alone, therefore ‘direct’ perception. His theory intimates that we see the world as a whole as part of a broad context and not as separate parts. He emphasises the dynamic nature of perception as evolving and changing which highlights the capacity to see our environment from different perspectives. In contrast to Gregory’s theory, Gibson asserts that illusions are artificial and occur in the context of the experiment, by removing people from their natural environment. Illusions could also be explained in terms that everything is available solely in the stimulus. Day elaborates on this by clarifying that the Müller-Lyer illusion is a result of perceptual compromise between the actual length of the line and the complete figure of which it is a part. Bruce offers that Gibson’s theory is reasonable in light of visually guided behaviour, for example, a frog only needs to sense a fly in order to guide the tongue to catch it, it does not need to form hypotheses about the fly, just sense and react. It’s likely that direct perception and Gregory’s theory co-exist in that they are describing different aspects of perception. Gibson’s theory is valuable as it emphasises the richness of the perceptual environment.
