Perceptual load theory

The perceptual load theory was originated by Nilli Lavie in the mid-nineties[1][2] in order to resolve the debate in attention research on the role of attention in information processing.[3][4][5] The question of the debate was whether attention affects information processing at early stages of perception (the ‘early selection’ view) or only at later stages such as memory or response selection (‘the late selection’ view). Accordingly, the debate is often called ‘the early and late selection’ debate. Perceptual load theory stipulates that perception has limited capacity but operates in automated, involuntary manner on all the information within its capacity. In other words, all the information that can be perceived (within the brain’s limited capacity) will be perceived. In tasks involving a large amounts of information, in other words high perceptual load, capacity is fully exhausted by the processing of the attended information, resulting in no perception of unattended information (‘early selection’). In contrast, in tasks of low perceptual load, since perception cannot be voluntarily stopped, spare capacity from processing the information in the attended task will inevitably spill over, resulting in the perception of task-irrelevant information that people intended to ignore (‘late selection’).

The theory resolves the early and late selection attention debate by explaining that tasks of low perceptual load result in late selection effects of attention, whereas tasks of high perceptual load result in early selection attention effects.

Key Assumptions

Perceptual load theory is a hybrid model, combining a limited capacity approach with a parallel simultaneous processing approach where perception proceeds in parallel on all information within its limited capacity until capacity runs out.[3][4][5][6][7] Voluntary control is limited in the theory to setting up priorities so that processing of stimuli that are relevant to the current task is prioritized over those that are irrelevant. However, what dictates whether a stimulus is processed or not is the level of load in the task. Irrelevant stimuli are still perceived in conditions of low perceptual load, despite their low priority.[3][4][5][6][7][8] From 2000 onwards Load theory was expanded to explain the interaction between perceptual load and load on cognitive control processes that actively maintain task priorities.[7][8][9]

‘High’ versus ‘Low’ Load

The distinction between ‘low’ and ‘high’ load displays is relative, rather than absolute.[1][3][4] The level of perceptual load can be raised by increasing the number of task units (for example the number of words in a word search task or the number of letters in a letter search task, or increasing the tasks demands for the processing each of these items. For example, a low-load task may involve searching for a target that has a distinguishing feature (such as colour), whereas a high-load task may involve a conjunction search, where the target is defined by a combination of features (such as colour and shape) which makes it harder to detect it.[3]

Under conditions of ‘low’ perceptual load, the theory predicts that any remaining capacity that has not been allocated to the processing of relevant stimuli will ‘spill over’ to task-irrelevant stimuli.[1][3][4][5][6][7] This ‘spillover’ under low-load conditions is seen as automatic and inevitable, thus not under voluntary control.[1] The allocation of attention and subsequent perceptual processing is prioritised so that stimuli designated as task-relevant are attended before task-irrelevant stimuli, continuing in this order until the capacity is exhausted.[1][3][4][5] Therefore, the theory asserts that irrelevant items such as distractors will only be perceived, and cause interference, under conditions of low load, when perceptual capacity has not been used up in the processing of relevant items.

Conversely, ‘high’ perceptual load displays involve either a larger set of relevant items to search, or require more information to process each item. These increased processing demands prevent irrelevant, low-priority items from consuming scarce processing capacity, which results in less distractor interference, as there is no remaining processing capacity for them to be perceived.[1][3] According to the theory, this results in the effective rejection of task-irrelevant distractors in high-load displays.[2]

Perceptual load research

Perceptual load theory received support from many studies that varied perceptual load in the task and found that distractor processing[3][5][9][10][11] and measures of perception and awareness[11][12][13] all depend on the level of perceptual load in the task. Brain imaging studies also found much evidence that brain response to a variety of unattended stimuli (ranging from motion to emotion) is modulated by the level of perceptual load in the attended task[14][15][16][17][18][19][20] Even the brain response related to novelty was found to be modulated by the level of perceptual load in the task.[21]

Criticisms

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The bulk of the evidence that accumulated since the mid nineties provides strong support for the perceptual load theory.[9][10][15] The few criticisms that were made recently typically target just one of the tasks termed the Eriksen Flanker task that was used to research load theory.[22]

See also

References

  1. 1 2 3 4 5 6 Lavie N. (1994) Perceptual load and physical distinctiveness as determinants of the locus of attentional selection. PhD Thesis, (Tel Aviv).
  2. 1 2 Lavie, Nilli (2011) Q&A. Current Biology, Volume 21, Issue 17, R645 - R647
  3. 1 2 3 4 5 6 7 8 9 Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Performance, 21, 451-468.
  4. 1 2 3 4 5 6 Lavie, N. & Tsal, Y. (1994). Perceptual load as a major determinant of the locus of selection in visual attention. Perception & Psychophysics, 56, 183-197.
  5. 1 2 3 4 5 6 Lavie, N. & Cox, S. (1997). On the efficiency of attentional selection: Efficient visual search results in inefficient rejection of distraction. Psychological Science, 8, 395-398.
  6. 1 2 3 Lavie, N. (2001). The role of capacity limits in selective attention: Behavioural evidence and implications for neural activity. In J. Braun & C. Koch (Eds.). Visual Attention and Cortical Circuits. pp. 49-68. Cambridge, Massachusetts: MIT press.
  7. 1 2 3 4 Lavie, N. (2000). Selective attention and cognitive control: dissociating attentional functions through different types of load. In S. Monsell & J. Driver (Eds.). Attention and performance XVIII, pp. 175-194. Cambridge, Massachusetts: MIT press.
  8. 1 2 Lavie, N., Hirst, A., De Fockert, J. W. & Viding, E. (2004) Load theory of selective attention and cognitive control. Journal of Experimental Psychology: General, 133, 339-354.
  9. 1 2 3 Lavie, N. (2005) Distracted and confused?: selective attention under load. Trends in Cognitive Sciences, 9, 75-82.
  10. 1 2 Lavie, N. (2010) Attention, Distraction and Cognitive Control under Load. Current Directions in Psychological Science, 19(3), 143-158
  11. 1 2 Forster, S. & Lavie, N. (2008). Failures to Ignore Entirely Irrelevant Distractors: The Role of Load. Journal of Experimental Psychology: Applied, 14, 73-83.
  12. ↑ Lavie, N. Lin, Z. Zokai, N. & Thoma, V (2009). The role of perceptual load in object recognition. Journal of Experimental Psychology: Human Perception and performance 21(1), 42-57.
  13. ↑ Macdonald J. & Lavie, N. (2008). Load induced blindness. Journal of Experimental Psychology: Human Perception and performance. 34(5), 1078-1091.
  14. ↑ Cartwright-Finch, U. and Lavie, N. (2007). The role of perceptual load in Inattentional Blindness. Cognition. 102(3), 321-340
  15. 1 2 Lavie, N., Beck, D. M. & Konstantinou, N. (2014). Blinded by the load: attention, awareness and the role of perceptual load. Philosophical Transactions of the Royal Society B: Biological Sciences, 369 (1641).
  16. ↑ Rees, G., Frith, C., & Lavie, N. (1997). Modulating irrelevant motion perception by varying attentional load in an unrelated task. Science, 278, 1616-1619.
  17. ↑ Schwartz, S., et al. (2005). Attentional load and sensory competition in human vision: modulation of fMRI responses by load at fixation during task-irrelevant stimulation in the peripheral visual field. Cerebral Cortex, 15, 770–786.
  18. ↑ O’Connor, D. H., Fukui, M. M., Pinsk, M. A., & Kastner, S. (2002). Attention modulates responses in the human lateral geniculate nucleus. Nature Neuroscience, 5, 1203–1209.
  19. ↑ Pinsk, M. A., Doniger, G. M., & Kastner, S. (2004). Push-pull mechanism of selective attention in human extrastriate cortex. Journal of Neurophysiology, 92, 622-629.
  20. ↑ Bishop, S. J., Jenkins, R., & Lawrence, A. (2007) The neural processing of task-irrelevant fearful faces: Effects of perceptual load and individual differences in trait and state anxiety. Cerebral Cortex, 17, 1595–1603.
  21. ↑ Yi, D-J., Woodman, G. F., Widders, D., Marois, R., & Chun, M. M. (2004). Neural fate of ignored stimuli: Dissociable effects of perceptual and working memory load. Nature Neuroscience, 7, 992–996.
  22. ↑ Lavie, Nilli; Torralbo, Ana (2010-12-01). "Dilution". Journal of Experimental Psychology. Human Perception and Performance. 36 (6): 1657–1664. doi:10.1037/a0020733. ISSN 0096-1523. PMC 3002221Freely accessible. PMID 21133554.
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