Perceptual load theory

Nilli Lavie presented the perceptual load theory in the mid-nineties as a potential resolution to the early/late selection debate.[1][2] This debate can be summated through two questions, firstly; when in the information processing stream does attention select target information? Secondly; to what degree do distractor stimuli get processed? Prior to Lavie’s theory there were several other suggestions as to how targets are perceived amongst distractor stimuli.

Researcher’s such as Donald Broadbent [3] argued that selection occurs during the early stages of processing by suggesting that information has to go through a sensory filter, and as that filter has a limited capacity all information that is not directly attended to will decay. Whilst researchers such as Deutsch and Deutsch argued that this filtering [4] of irrelevant stimuli occurs in the late stages of processing, in that, all of the information is processed on a sensory level but just before the level of working memory the semantic content of the message is the filter. Lavie attempts to resolve this debate by stating that both early and late selection occur varying on the stimulus presented.

From the perspective of perceptual load theory stimulus variation means whether the stimulus has high or low perceptual load. Perceptual load refers to the complexity of the physical stimuli, particularly the distractor stimuli e.g. a square surrounded by circles is a scene with low perceptual load whereas a square surrounded by lots of different shapes has high perceptual load. Due to the assumed limited capacity of attentional resources and that distractors have to be processed before the target it is suggested that, in high load tasks the targets attentional resources are depleted faster therefore being able to attend to the target sooner compared to a low load task. This is because the low load task needs to process more of the distractors to exhaust mental resources, therefore the distractors cause a greater inference in finding the target. This demonstrates that selection occurs both in the early stages of processing (high load condition) when the degree of inference is low as the majority of the resources process the target and enables the individual to ignore distractors. As well as the late stages (low load condition) when the distractors are perceived because they take up fewer attentional resources and as such spill over to the distractors which results in them being perceived, causing an interference.[5][6][7][8]

Key assumptions

Perceptual load theory makes three main assumptions, these are;[1][2]

  1. Attentional resources are limited in capacity.
  2. Task-relevant stimuli are processed before task-irrelevant stimuli.
  3. That all of the attentional resources have to be used up.

Therefore, if the task-relevant stimulus uses all of the attentional resources then none of the task-irrelevant stimuli (distractors) will be processed.

Criticisms

In spite of the collection of research that has accumulated over the 90’s and early 2000’s there has been a counter argument posited by Lavie’s PhD supervisor, Tsal Yehoshua. However, it should be noted that in spite of the relevance of Tsal’s critique some of the first critiques to the perceptual load theory pointed out how a visual cue can eliminate the inference effect supposedly created by perceptual load.[9][10]

Dilution Effects

Primarily; the critique that Tsal makes is that perceptual load theory is not a solution to the early selection versus late selection debate but rather is purely an early selection model.[11] The suggested reason that causes the inference rates to change between simple versus complex displays is dilution not load.[12] Meaning that the high load condition has lower inference because the higher number/more complex distractors, not because of perceptual load. This was tested in a series of experiments [12] which took the classic perceptual load experiments [1] and added a new condition, the dilution condition. The way this condition varied is that it makes the distractors in the task the same colour, and making that colour differ from the target letter. This creates a condition that is low in load, and high in dilution and thus isolates dilution as a variable. The result of this manipulation was not that of a higher inference rate in low perceptual load conditions comparative to high as seen in the original perceptual load experiments. Rather that inference levels were significantly lower in the low load and dilution conditions compared to the high load.

Distractor Salience

Another proposed theory to explain results attained by Lavie’s original experiments is that of distractor salience.[13] As the title suggests this theory concerns the salience, or prominence, of a distractor as being the primary factor in inducing these results instead of load. By manipulating the onset versus offset of the distractor, research displayed the effect of salience on selective information. In this research onset and offset differed in terms of when the distractor was presented, either simultaneously with the singleton search task (onset) or having it appear with a fixation point before the task (offset). This resulted in an inference effect on reaction times when searching for the target in the onset condition regardless of whether the trial was a high load trial or a low load trial. This demonstrates that the effect seen in Lavie’s work [1] is not as a result of load manipulation, but of distractor salience.

Methodological Issues

There are also some crucial methodological issues with perceptual load theory research pertaining to experimental design.[2][5][6][7][8] Specifically, the use of a blocked design compared to a mixed design in the experiments. In this case, blocked experimental design is when all of the trials with either low or high perceptual load are carried out sequentially within a block of trials. Whereas, a mixed experimental design has combination of both low and high perceptual load trials that are randomly intermixed within a block of trials. The issue with using a blocked design is that the repetition of the same experimental condition can allow for attention to be localised in one particular spot. Research has shown that when conducting a perceptual load task under a mixed design there is no significant difference in interference between low load and high load conditions.[14] Therefore, suggesting that when the trials are blocked it is not perceptual load that causes the difference in interference rather how localised the participants field of attention was. This has since been expanded and developed by [15][16] and be coined as ‘Attentional Zoom’.

Attentional Zoom

As previously discussed attentional zoom was coined by researchers Zhe Chen and Kyle Cave as an alternative explanation to the results seen in perceptual load theory. The pair also critique other attempts into understanding the data presented by perceptual load theory, such as dilution.[15] Attentional zoom theory states that participants can process distractors when they are within their attentional focus. So when an individual is induced to have a small attentional focus and the distractors fall outside of them.[17] Likewise for a larger attentional focus that incorporates distractors a higher level of inference is seen. This can be demonstrated as separate from dilution as in [15] dilution through luminance decrease had no effect on distractor processing whilst being cued as to whether a target would appear in either one of two locations or one of six did. According to dilution theory the two trials should be show similar levels of inference regardless of cueing, however, what this experiment reveals is that when cued for two locations the attentional focus of the participants narrowed, thus reducing the effect of the distractor as it was outside the attentional view. Whereas, when the target was cued for six the attentional focus was forced to widen and as such the distractor could be processed causing an inference effect.

See also

References

  1. 1 2 3 4 Lavie, Nilli; Tsal, Yehoshua (1994). "Perceptual load as a major determinant of the locus of selection in visual attention" (PDF). Perception and Psychophysics. 56 (2): 183–197. doi:10.3758/bf03213897. Retrieved 2 June 2017.
  2. 1 2 3 Lavie, Nilli (1995). "Perceptual load as a necessary condition for selective attention" (PDF). Journal of Experimental Psychology: Human Perception and Performance. 21 (3): 451–468. doi:10.1037/0096-1523.21.3.451. Retrieved 2 June 2017.
  3. ↑ Broadbent, Donald. E (1958). Perception and Communication. New York: Oxford University Press.
  4. ↑ Deutsch, J. A.; Deutsch, D (Jan 1963). "Attention: some theoretical considerations". Psychological Review. 70 (1): 80–90. doi:10.1037/h0039515.
  5. 1 2 Cartwright-finch, Ula; Lavie, Nilli (2007). "The role of perceptual load in inattentional blindness". Cognition. 102 (3): 321–340. doi:10.1016/j.cognition.2006.01.002. PMID 16480973.
  6. 1 2 Lavie, Nilli; Hirst, A; de Fockhert, J. W; Viding, E (2004). "Load theory of selective attention and cognitive control". Journal of Experimental Psychology. 133 (3): 339–354. doi:10.1037/0096-3445.133.3.339. PMID 15355143.
  7. 1 2 Lavie, Nilli (Feb 2005). "Distracted and confused?: Selective attention under load". Trends in Cognitive Sciences. 9 (2): 75–82. CiteSeerX 10.1.1.393.1015. doi:10.1016/j.tics.2004.12.004. PMID 15668100.
  8. 1 2 Rees, G; Frith, CD; Lavie, Nilli (Nov 1997). "Modulating irrelevant motion perception by varying attentional load in an unrelated task". Science. 278 (5343): 1616–1619. doi:10.1126/science.278.5343.1616. PMID 9374459.
  9. ↑ Johnson, D. N.; McGrath, A.; McNeil, C. (2002). "Cuing interacts with perceptual load in visual search". Psychological Science. 13 (3): 284–287. doi:10.1111/1467-9280.00452. PMID 12009052.
  10. ↑ Paquet, L; Craig, G. L (1997). "Evidence for selective target processing with a low perceptual load flankers task". Cognition. 25 (2): 182–189. doi:10.3758/bf03201111.
  11. ↑ Benoni, H; Tsal, Y (2013). "Conceptual and methodological concerns in the theory of perceptual load". Frontiers in Psychology. 4: 522. doi:10.3389/fpsyg.2013.00522. PMC 3741554. PMID 23964262.
  12. 1 2 Tsal, Y; Benoni, H (2010). "Where have we gone wrong? Perceptual load does not affect selective attention". Vision Research. 50 (13): 1292–1298. doi:10.1016/j.visres.2010.04.018. PMID 20430048.
  13. ↑ Eltiti, Stacy; Wallace, Denise; Fox, Elaine (2005). "Selective target processing: Perceptual load or distractor salience?". Perception and Psychophysics. 67 (5): 876–885. doi:10.3758/bf03193540.
  14. ↑ Murray, Janice E; Jones, Craig (2010). "Attention to local form information can prevent access to semantic information". The Quarterly Journal of Experimental Psychology. 55 (2): 609–625. doi:10.1080/02724980143000370. PMID 12047062.
  15. 1 2 3 Chen, Zhe; Cave, Kyle R (June 2013). "Perceptual load vs. dilution: the roles of attentional focus, stimulus category, and target predictability". Frontiers in Psychology. 4: 1–14. doi:10.3389/fpsyg.2013.00327. PMC 3675768. PMID 23761777.
  16. ↑ Chen, Zhe; Cave, Kyle R (2016). "Identifying Visual Targets Amongst Interfering Distractors: Sorting Out the Roles of Perceptual Load, Dilution, and Attentional Zoom". Attention, Pereception, and Psychophsics. 78 (7): 1822–38. doi:10.3758/s13414-016-1149-9. PMID 27250363.
  17. ↑ Eriksen, Charles W; St James, J. D. (1986). "Visual attention within and around the field of focal attention: A zoom lens model". Perception and Psychophysics. 40 (4): 225. doi:10.3758/BF03211502.
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