Stephen Pierzchajlo defends his thesis on olfaction
Thesis defence
Date: Friday 17 October 2025
Time: 13.00 – 15.00
Location: Lecture Room 16, Albano
On 17 October Stephen Pierzchajlo will defend his doctoral thesis "Smelling Without A Smell: How olfactory-perceptual representations are activated by words".
The dissertation will take place on Friday 17 October 2025 at 13:00 in Lecture Room 16, House 2, Albano, Stockholm.
Opponent: Professor Moustafa Bensafi, Lyon Neuroscience Research Center, Frankrike.
Supervisors: Professor Jonas Olofsson, Department of Psychology, Stockholm University.
Contact: Jonas Olofsson
Read more about Stephen Pierzchajlo
Abstract
We spend every day using our senses to interact with the world. Though we use language as a way to understand the sensory world, language might have different roles for different senses. Freely identifying odors in naming tasks is more difficult than with senses like vision, making olfaction an interesting place to study the intersection between language and the senses. While free olfactory identification is poor, word cues strongly increase our ability to identify odors. This has led some to conclude that olfaction is more dependent on supporting information from other senses, and that odors are encoded in a coarse way, so it is particularly dependent on language and sensory cues to function capably. This has further led to debate regarding whether language can activate olfactory-related representations in the brain, or whether odor and language systems are disconnected. The general aim of this thesis was to investigate whether and how word cues can affect olfactory processes and representations.
Study I investigated whether the olfactory system is more reliant on object-based predictive verbal cues than the visual system. Using two behavioural experiments and one neuroimaging experiment, Study I found that reaction time is most delayed when words incorrectly cue an (unexpected) odor target. Study I further demonstrated that the primary and secondary olfactory cortices are more activated by odors that were unexpected, something similar to predictive coding in the visual system, but also that visual and cognitive activations were observed by unexpected odors. Study II investigated whether word cues could activate olfactory representations similar to actual odor perception. Using an in-person olfactory psychophysics experiment, an online experiment, and embeddings from a custom trained Large Language Model, Study II found that odor similarity scores estimated from odor names were very strongly correlated with their odor-based counterparts, and that this correlation was only mediated to a small degree by the semantic similarity of the word pairs, suggesting word-based representations of odors closely resemble odor representations. Study III assessed whether people can make accurate judgements about odor similarities based on viewing words and when effective odor imagery was prevented by nose blocking. Study III found that people can very accurately determine how similar two odors are using only word cues, and that people can seemingly do this when their nose is blocked.
Overall, this research supports the idea that there are unique mechanisms whereby word cues guide olfactory processes, and that odor representations can be accessed by perceiving odor names, without the presence of odors or elicited vivid mental images of odors. Even though odors are often hard to name or describe verbally, olfaction may thus be strongly shaped by language cues.
Last updated: October 3, 2025
Source: Department of Psychology