For years there have been questions about whether we see the same colours, hear the same sounds, smell the same odours. How can we tell what someone else experiences in their conscious awareness? Well plainly, today at least, we can’t tell what someone else experiences.
But multivariate pattern analyses gives a type of decoding of patterns of activity in the brain. It has been used to do a type of ‘mind reading’ – but with the disadvantage that the code to ‘read’ a particular perception or thought is highly personal. The activity pattern resulting from a particular picture will be decoded only after many examples of pictures have been studied in that individual to create a decoding program. This tell us nothing (or very, very little) about how our perceptions may be similar.
Sight, hearing and smell are complex domains, and so it is not surprising that the activity patterns are individual. But taste has only a handful of qualities (sweet, salty, sour, bitter, savory) compared to extremely large numbers of qualities in colour, pitch and basic odours. Of course a perception has added qualities of intensity, has various mixtures of the basic qualities, and has emotional overtones. Still a low number of basic qualities and a restricted range of intensities gives a much more tractable decoding program. Taste can also be analysed early in its perception and some of the pattern’s elements are ‘hardwired’. The Crouzet paper (abstract below) has highlights: “large-scale electrophysiological response patterns code for taste quality in humans; taste quality is represented early in the central gustatory system; neural response patterns correlate with subjective perceptual experience.”
If it is further found in future research that these patterns are similar for different individuals tasting the same taste, then it would raise the probability that our experiences of other senses are also similar. If the patterns for different individuals show no similarity, then the probability that we share qualia is low.
Here is the abstract of the paper (S. Crouzet, N. Busch, K. Ohla; Taste Quality Decoding Parallels Taste Sensations; 2015 Current Biology):
“In most species, the sense of taste is key in the distinction of potentially nutritious and harmful food constituents and thereby in the acceptance (or rejection) of food. Taste quality is encoded by specialized receptors on the tongue, which detect chemicals corresponding to each of the basic tastes (sweet, salty, sour, bitter, and savory), before taste quality information is transmitted via segregated neuronal fibers, distributed coding across neuronal fibers, or dynamic firing patterns to the gustatory cortex in the insula. In rodents, both hardwired coding by labeled lines and flexible, learning-dependent representations and broadly tuned neurons seem to coexist. It is currently unknown how, when, and where taste quality representations are established in the cortex and whether these representations are used for perceptual decisions. Here, we show that neuronal response patterns allow to decode which of four tastants (salty, sweet, sour, and bitter) participants tasted in a given trial by using time-resolved multivariate pattern analyses of large-scale electrophysiological brain responses. The onset of this prediction coincided with the earliest taste-evoked responses originating from the insula and opercular cortices, indicating that quality is among the first attributes of a taste represented in the central gustatory system. These response patterns correlated with perceptual decisions of taste quality: tastes that participants discriminated less accurately also evoked less discriminated brain response patterns. The results therefore provide the first evidence for a link between taste-related decision-making and the predictive value of these brain response patterns.”
Note: Kathrine Ohla sent this
I just came across your blog entry "looking for qualia" and like to thank you for discussing our work. I am glad it raises so much interest also outside the "taste community". If it's not too much to ask, I would appreciate if you included the hyperlink to the paper. This would allow your readers to find the full article quicker. http://dx.doi.org/10.1016/j.cub.2015.01.057