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As soon as you taste it: evidence for sequential and parallel processing of gustatory information

The quick and reliable detection and identification of a tastant in the mouth regulate nutrient uptake and toxin expulsion. Consistent with the pivotal role of the gustatory system, taste category information (e.g., sweet, salty) is represented during the earliest phase of the taste-evoked cortical response (Crouzet et al., 2015), and different tastes are perceived and responded to within only a few hundred milliseconds, in rodents (Perez et al., 2013) and humans (Bujas, 1935). Currently, it is unknown whether taste detection and discrimination are sequential or parallel processes, i.e., whether you know what it is as soon as you taste it. To investigate the sequence of processing steps involved in taste perceptual decisions, participants tasted sour, salty, bitter, and sweet solutions and performed a taste-detection and a taste-discrimination task.
 

Wallroth 2018

Figure 1. Schematic illustration of the experimental design during the detection and discrimination tasks. During each trial, a liquid tastant (black) was embedded in a sequence of water pulses. Participants were to speededly respond by button press during both tasks.

 


We measured response times (RTs) and 64-channel scalp electrophysiological recordings and tested the link between the timing of behavioral decisions and the timing of neural taste representations determined with multivariate pattern analyses. Irrespective of taste and task, neural decoding onset and behavioral RTs were strongly related, demonstrating that differences between taste judgments are reflected early during chemosensory encoding. Neural and behavioral detection times were faster for the iso-hedonic salty and sour tastes than their discrimination time. No such latency difference was observed for sweet and bitter, which differ hedonically. Together, these results indicate that the human gustatory system detects a taste faster than it discriminates between tastes, yet hedonic computations may run in parallel (Perez et al., 2013) and facilitate taste identification.

Wallroth 2018

Figure 2. A. Average within-subject decoding generalization across time for each of the four tastes by task. Salty and sour show earlier and better detection performance than sweet and bitter, whereas discrimination performance is less pronounced than detection performance in either case. B. Behavioral data of the button press RTs of correct
responses and accuracy color-coded for tasks (blue indicating detection trials, gray discrimination trials). Participants are faster and more accurate at detecting salty and sour than they are at discriminating the two tastants. Sweet and bitter show no difference in RTs but higher accuracy at discriminating the two as opposed to detection from water. C. Neural data of onset times of above-chance performance and of the accuracy indicating the percentage of trials for which such an onset was determinable. The neural findings correspond closely to the behavioral data in that salty and sour are classified faster and more accurately in detection trials. Sweet and bitter show no significant difference between the two tasks.


Publication:

Wallroth, R. & Ohla, K. (2018). As soon as you taste it: evidence for sequential and parallel processing of gustatory information. eNeuro, 5(5), e0269-18.2018 1–11


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