fMRI and Task Load

This section looks at the differences between perceptual demands and working memory demands.

Rees, Frith and Lavie (1997)

• They assessed brain activity in motion related areas (V5) during changes in demands of a linguistic task
• Participants were asked to focus on single words that were successively, presented on screen. They were also told to ignore the white dots in the periphery.
• The white dots were either static or moving
• in the low load condition, they had to press a key for uppercase
• In the high load task they had to press a key for bisyllabic words
• Results: The mean activity in the V5 (motion detection area) was measured under different perceptual loads.
• In the low load example, irrelevant motion was detected. This did not occur in the high load task however. This is because selective attention only appears to be possible under high loads, as there is a higher allocation of cognitive resources to the task.

Yi et al. (2004)

• 'Neural fate of ignored stimuli: perceptual vs working memory demands'
• Participants were presented with a series of images, including a picture of a person, and had to identify whether the current face is the same as the one before or the same as two before (2 before=high working memory load)
• The degraded stimuli condition (high perceptual load) should reduce the amount of perceptual attention that is available for processing the background (house)
• The study also looked at how much the scenes were processed when they were repeated, or not repeated.
• Results: These showed low perceptual demand and high working memory load. There was greater activation in the parahippocampal place area (PPA) for the unrepeated condition suggesting that there was more processing of the background.
• In the high perceptual demand task, where there was degraded stimuli, the task irrelevant stimuli were easier to ignore.

Perceptual Load vs. working memory load:

• When perceptual load is high, early selection takes place, and there is good selectivity, meaning that the background is not likely to be processed.
• When there is a high working memory load, late selection takes place and selectivity is much poorer, meaning that the background is processed more.
• Cognitive load refers to perceptual load and working memory load combined