The “Attentional Spotlight” Metaphor Of Visual Perception
Focused visual attention refers to the attention one gives to an object or area within a given space. Some have likened this to a spotlight, because we preferentially process whatever falls into our beam of focus (Muller, Malinowski, Gruber and Hillyard, 2003).
However, rather than being stationary, research carried out by Posner, Snyder and Davidson (1980) suggests that this “attentional spotlight” may in fact be continually scanning our environment, drawing our attention to stimuli within our field of view via an endogenous, or conscious, system, and to stimuli outside our field of view via an exogenous, or unconscious, system.
Brain imaging scans do seem to support the idea of multiple attentional systems (Rapp, 2001), which in turn opens up the possibility that the characteristics of the attentional spotlight may vary depending on which system is activated.
LaBerge (1983) for example, found that attention could be focused on the space of one letter or of a whole word, which seems to indicate that the width of the attentional spotlight may be altered depending on the stimulus in question (Eysenck and Keane, 2010).
There does however, appear to be a minimum width, as a letter within one degree of another letter can not be excluded from attention (Eriksen and Eriksen, 1974).
As for the maximum width of the attentional spotlight, some studies have shown that unattended stimuli do produce brain activity (Wojciulik, Kanwisher and Driver, 1998), however, this activity is significantly less than for attended stimuli (Morgan and Desimone, 1985) suggesting that some inhibitory mechanism may be involved in preventing unattended stimuli from capturing ones attention (Prime and Ward, 2004).
Two inferences may be made from these findings. The first is that there is no maximum width of the attentional spotlight. It sees all, but selectively filters what it brings to attention.
A second, and perhaps more likely possibility, is that there are multiple spotlights scanning localised regions of the visual field which bring to attention stimuli through a process of summation, whereby summated excitatory signals capture attention and summated inhibitory signals repress it.
Evidence for this later proposal comes from Castiello and Umilta (1992) who showed that focal attention can indeed be split, contrary to findings by Eriksen and Yeh (1985), but that this division of focal attention only occurs in opposite sides of the visual field.
Similar research carried out by Awh and Pashler (2000) supports these findings, showing that attention can be split, but only when stimuli are not directly next to each other.
Furthermore, neuroimaging data has shown that separate areas of the visual cortex become stimulated when attention is divided between two stimuli as opposed to one (Tong, 2004), providing a neurological argument against the idea of a single attentional spotlight.
There does however, appear to be a limit to the division of attention. Sears and Pylyshyan (2000) for example, found that four stimuli could be attended to simultaneously, although for tasks which are mentally demanding, division of attention does not appear to occur at all (Joseph, Chun and Nakayama, 1997).
This suggests that there may in fact be different attentional systems that are activated or deactivated in response to certain stimuli, and that attention itself is a finite resource that must be divided amongst the stimuli being processed (Styles, 2006).
It could be argued however, that attention is not a finite resource, but rather is filtered for relevant and irrelevant stimuli (Broadbent, 1982).
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