Does expectation affect brain responses to repeated objects?
When people expect to see an object repeated, the brain's visual processing regions show a significantly reduced response, but only in the left hemisphere.
Source
Neural repetition suppression: evidence for perceptual expectation in object-selective regions
Study at a glance
- Design
- Human experiment — fMRI repetition suppression in object-selective cortex as a function of perceptual expectation; localizer in a subset
- N
- N=19 · University of Salzburg undergraduates, 11 women, ages 18–30; 16 completed a functional localizer
- Population
- Healthy undergraduates with normal or corrected vision
- Outcome
- Repetition-suppression in object-selective cortex supporting perceptual expectation
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Does expectation affect brain responses to repeated objects?
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
19 healthy young adults were scanned in this study
Nineteen undergraduate students (11 female) from the University of Salzburg (age 18–30 years) participated in the present study.
75% of the stimulus pairs in the high-probability context contained repeated images
In the high-probability context, images were the same in 75% of trials.
What they did
To see if visual expectation influences how the brain processes repeated objects, researchers scanned 19 healthy young adults using fMRI. Participants viewed pairs of object drawings where the second image was either identical or different, presented across two contexts: a high-probability context where 75% of the pairs contained repeated images, and a low-probability context where only 25% did. To identify specific brain regions of interest, 16 of the participants also completed a functional localizer scan.
What they found
The researchers discovered that expectation heavily modulated repetition suppression, but only in the left hemisphere of the brain. In the left lateral occipital complex, expected repetitions caused a 21% reduction in neural activity, whereas unexpected repetitions led to a 1% increase in activity. In contrast, the right hemisphere and other specialized brain regions did not show this expectation-dependent modulation.
The limits
What it doesn't show
The study's results are limited by its small sample size of 19 university students, meaning these findings might not apply to more diverse age groups. Because the lateralization effect was unexpected, this study cannot explain why expectation-based modulation of repetition suppression occurred exclusively in the left hemisphere. Additionally, since participants performed a passive target-detection task, the design cannot clarify how active engagement or goal-directed attention might influence these neural responses.
Key terms
- Repetition suppression
- A reduction in neural activity that occurs when a stimulus is presented to the brain multiple times.
- Predictive coding
- A theoretical framework suggesting the brain constantly generates and updates a mental model of the environment to predict sensory input.
- Lateral occipital complex (LOC)
- A region in the human visual cortex that plays a critical role in object recognition.
- Fusiform face area (FFA)
- A specialized region in the temporal lobe that is highly selective for processing human faces.
- Parahippocampal place area (PPA)
- A region in the brain's visual pathway that responds preferentially to environmental scenes and places.
- Hemodynamic response
- The rapid delivery of oxygen-rich blood to active neural tissue, measured in fMRI as the BOLD signal.
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How is repetition suppression (RS) commonly defined in functional neuroimaging?
Common questions
Why did the researchers look at face- and place-selective brain areas as controls?
The authors wanted to test whether expectation effects are highly specific to the regions that process that exact stimulus category, or if they represent a more general, widespread brain response.
Why did this study find an expectation effect for objects when previous studies did not?
The researchers used a larger difference in repetition probability between contexts to make the expectations stronger, and they required participants to actively pay attention to the objects rather than a central fixation point.
What is the difference between repetition suppression and repetition enhancement?
Repetition suppression refers to a decrease in brain activity when a stimulus is repeated, whereas repetition enhancement is an increase in brain activity when a stimulus is repeated.
How might internal verbalization explain the left-hemisphere lateralization?
Participants may have mentally named the expected objects in their heads, and since language processing is typically dominant in the left hemisphere of the brain, this could have restricted the expectation effect to that side.
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