HAL Id: hal-01761971
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Submitted on 9 Apr 2018
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without Perceptual Awareness
Leonardo S. Barbosa, Sid Kouider
To cite this version:
Leonardo S. Barbosa, Sid Kouider. Prior Expectation Modulates Repetition Suppression without Per-
ceptual Awareness. Scientific Reports, Nature Publishing Group, 2018, 8, pp.5055. �10.1038/s41598-
018-23467-3�. �hal-01761971�
Prior Expectation Modulates
Repetition Suppression without Perceptual Awareness
Leonardo S. Barbosa
1,2& Sid Kouider
1Stimulus repetition induces attenuated brain responses. This phenomenon, termed repetition suppression (RS), is classically held to stem from bottom-up neuronal adaptation. However, recent studies suggest that RS is driven by top-down predictive mechanisms. It remains controversial whether these top-down mechanisms of RS rely on conscious strategies, or if they represent a more fundamental aspect of perception, coding for physical properties of the repeated feature. The presence of top- down effects in the absence of perceptual awareness would indicate that conscious strategies are not sufficient to explain top-down mechanisms of RS. We combined an unconscious priming paradigm with EEG recordings and tested whether RS can be modulated by the probability of encountering a repetition, even in the absence of awareness. Our results show that both behavioural priming and RS near occipital areas are modulated by repetition probability, regardless of prime awareness.
This contradicts previous findings that have argued that RS modulation is a by-product of conscious strategies. In contrast, we found that the increase in theta-band power following unrepeated trials – an index of conflict detection – is modulated only by expectations during conscious primes, implicating the use of conscious strategies. Together, our results suggest that the influence of predictions on RS can be either automatic in sensory brain regions or dependent on conscious strategies.
Neural activity induced by a stimulus is usually reduced when it is repeated. This phenomenon, termed repetition suppression (RS), is classically attributed to neuronal adaptation
1,2. RS has been traditionally assumed to result from a bottom-up modulation of neuronal sensitivity to the stimulus, either as a consequence of neuronal fatigue or through the sharpening of neural representations. For this reason, RS has been extensively used to investigate neuronal selectivity across a variety of recording modalities
1,3. Simply put, the neurons showing a decrease in sensitivity following the repetition of a specific feature (e.g. shape, orientation, etc.) are assumed to code for this feature
4,5.
However, RS has recently been argued to derive from top-down predictive mechanisms. From this perspective, perception emerges as a comparison between top-down activity (reflecting the expected percept) and bottom-up activity (resulting from the observed sensory evidence). The overall activity elicited by a stimulus would reflect the difference between the expected and the actual stimulus
6,7. More specifically, the decrease in activity after the second presentation of a stimulus would be a consequences of a reduced ‘prediction error’ because this stimulus was previously seen and hence predicted (i.e., more probable), in comparison to a novel one
8,9. This predictive coding framework makes the important additional assumption that RS should increase with the likelihood of encountering a repetition. This repetition probability effect (RPE) has been shown not only for faces
9,10but also for auditory tones
11, suggesting that predictions play a crucial role in RS
12.
Yet, this interpretation has been challenged by a surge of recent studies showing RS unaffected by repeti- tion likelihood. For instance, while the RPE has been consistently reported for faces
9,10,13,14, it hardly generalizes to everyday objects, natural scenes and meaningless shapes such as fractals
15,16. Moreover, unlike RS, the RPE appears to vanish when the repeated stimulus becomes task-irrelevant
17. The lack of RPE while RS is maintained, casts doubts on predictive coding accounts of RS and suggest that the RPE results from the manifestation of explicit and conscious strategies
17.
However, it remains possible that the RPE requires conscious strategies only for building predictions and not for their use during online processing. Indeed, the predictive mechanisms underlying the RPE might require
1