Abstract
The subcortical sensory pathways are the fundamental channels for mapping the outside world to our minds. Sensory pathways efficiently transmit information by adapting neural responses to the local statistics of the sensory input. The long-standing mechanistic explanation for this adaptive behaviour is that neural activity decreases with increasing regularities in the local statistics of the stimuli. An alternative account is that neural coding is directly driven by expectations of the sensory input. Here, we used abstract rules to manipulate expectations independently of local stimulus statistics. The ultra-high-field functional-MRI data show that abstract expectations can drive the response amplitude to tones in the human auditory pathway. These results provide first unambiguous evidence of abstract processing in a subcortical sensory pathway. They indicate that the neural representation of the outside world is altered by our prior beliefs even at initial points of the processing hierarchy.
Highlights
Expectations have measurable effects on human perception; for instance, when disambiguating ambivalent stimuli like an object in the dark or spoken sentences in a noisy pub (de Lange et al, 2018)
Expectations for each of the deviant positions were manipulated by two abstract rules that were disclosed to the subjects: (1) all sequences have a deviant, and (2) the deviant is always located in positions 4, 5, or 6
Sensory processing can be explained by habituation to local stimulus statistics (Figure 1C, h1), in the other by predictive coding (Figure 1C, h2)
Summary
Expectations have measurable effects on human perception; for instance, when disambiguating ambivalent stimuli like an object in the dark or spoken sentences in a noisy pub (de Lange et al, 2018). SSA is often taken to support the view of predictive coding (Font-Alaminos et al, 2020; Carbajal and Malmierca, 2018; Malmierca et al, 2015; Cacciaglia et al, 2015), it can be explained in terms of habituation (Malmierca et al, 2014), where neurons show decreased responsiveness to increased regularities in their local statistics independently of their predictability (see Grill-Spector et al, 2006; Kok and de Lange, 2015 for reviews) These local effects have been proposed to be caused by synaptic fatigue (Wang et al, 2014), network habituation (Eytan et al, 2003; Mill et al, 2011), or sharpening of the receptive fields after stimulus repetition (GrillSpector et al, 2006); they occur even at the level of the retina (Hosoya et al, 2005) and the cochlea (Yates et al, 1990). We focused on the nuclei of the thalamus (medial geniculate body, MGB) and midbrain (inferior colliculus, IC) as they are the key nuclei of the ascending subcortical pathway that can be reliably investigated in human participants in vivo (Sitek et al, 2019)
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