Repetition Probability Does Not Affect fMRI Repetition Suppression for Objects

Abstract

Previously several functional magnetic resonance imaging (fMRI) studies point toward the role of perceptual expectations in determining adaptation or repetition suppression (RS) in humans. These studies showed that the probability of repetitions of faces within a block influences the magnitude of adaptation in face-related areas of the human brain (Summerfield et al., 2008). However, a current macaque single-cell/local field potential (LFP) recording study using objects as stimuli found no evidence for the modulation of the neural response by the repetition probability in the inferior temporal cortex (Kaliukhovich and Vogels, 2010). Here we examined whether stimulus repetition probability affects fMRI repetition suppression for nonface object stimuli in the human brain. Subjects were exposed to either two identical [repetition trials (RTs)] or two different [alternation trials (ATs)] object stimuli. Both types of trials were presented blocks consisting of either 75% [repetition blocks (RBs)] or 25% [alternation blocks (ABs)] of RTs. We found strong RS, i.e., a lower signal for RTs compared to ATs, in the object sensitive lateral occipital cortex as well as in the face-sensitive occipital and fusiform face areas. More importantly, however, there was no significant difference in the magnitude of RS between RBs and ABs in each of the areas. This is in agreement with the previous monkey single-unit/LFP findings and suggests that RS in the case of nonface visual objects is not modulated by the repetition probability in humans. Our results imply that perceptual expectation effects vary for different visual stimulus categories.

Repetition probability effects for inverted faces

“…Two studies, using non-face stimuli, found no evidences of repetition probability modulations of RS in the macaque inferior temporal cortex (Kaliukhovich and Vogels, 2011) and in the human lateral occipital cortex (Kovács et al, 2013). These results with natural objects, fractals and chairs as stimuli are in strong contrast with those studies which found a significant modulation of RS by P(rep) for faces (Summerfield et al, 2008;Kovács et al, 2012;Larsson and Smith, 2012) as well as for voices (Andics et al, 2013).…”

“…First of all, Kaliukhovich and Vogels (2011), using single-cell recordings in macaque monkeys, found no effect of P(rep) on RS. Similarly, Kovács et al (2013) showed an effect of stimulus expectation for faces but not for chairs and other every-day objects. Finally, Grotheer and Kovács (2014) found that P(rep) affects RS only for stimuli of expertise.…”

“…Altogether, these neuroimaging and electrophysiological studies suggest that the attenuated neural response for repeated stimuli is a direct neural correlate of reduced ε of the bottom-up and top-down representations, as suggested by the predictive coding models of neural functions (Friston, 2005). Note however, that the role of stimulus expectation in generating RS for non-face stimuli has been directly called into question by some recent studies (Grotheer and Kovács, 2014;Kaliukhovich and Vogels, 2011;Kovács et al, 2013; but for a different conclusion see Mayrhauser et al, 2014). First of all, Kaliukhovich and Vogels (2011), using single-cell recordings in macaque monkeys, found no effect of P(rep) on RS.…”

“…240 gray-scale, digital photos of full-frontal Caucasian faces, similar to the face stimuli of (Kovács et al, 2012;Kovács et al, 2013), were fit behind a circular mask (diameter=5.5°) and either presented upright (UPR), or inverted (INV) in different runs of fMRI recordings. No stimulus occurred in more than one trial during each run.…”

“…One possibility is that the extensive experience we have with faces leads to enhanced configural/holistic processing of stimuli (Bukach et al, 2006), which, in turn, gives rise to the P(rep) effects. In other words, theoretically it is possible that only the configural/holistic processing stages, which are specific for faces are affected by P(rep) and that this explains the face specificity of probability effects (Kaliukhovich and Vogels, 2011;Kovács et al, 2013).…”