Scent and Sensibility: Perception Shifts in the Olfactory Domain (2023)

Abstract: In this work, we investigate olfactory perception shifts, analysing how the description of the smells emitted by specific sources has changed over time. We first create a benchmark of selected smell sources, relying upon existing historical studies related to olfaction. We also collect an English text corpus by retrieving large collections of documents from freely available resources, spanning from 1500 to 2000 and covering different domains. We label such corpus using a system for olfactory information extraction inspired by frame semantics, where the semantic roles around the smell sources in the benchmark are marked. We then analyse how the roles describing Qualities of smell sources change over time and how they can contribute to characterise perception shifts, also in comparison with more standard statistical approaches.

## introduction over the past few decades, there has been a proliferation of studies in the realm of linguistics and perception @xcite . however, there remains a distinct shortage of research dedicated to the tracking of perceptual changes over time. although it has been already highlighted how much sensory language can be informative in terms of cultural attitudes @xcite , there has been a relatively limited exploration of how perceptual experiences are linguistically encoded over an extended period of time. a first attempt concerning the diachronic analysis of the olfactory domain using nlp has been presented in @xcite , although this study was rather exploratory and relied on an existing approach utilizing word embeddings. one of the reasons of the scarcity of studies using automatic approaches in this area is the difficult assessment of perceptual shifts due to the limited availability of suitable evaluation benchmarks. therefore, in this paper, we first introduce a manually created benchmark containing a list of smell sources (mainly objects) that underwent some changes in the way their odour was described over time. this benchmark is based upon existing literature in historical studies and olfactory cultural heritage. we then present some analyses of perception shifts that compare standard statistical approaches to a novel framework based on the output of a system for olfactory information extraction. our approach involves modelling perception shifts as changes in the association between a given smell source and its description in terms of (olfactory) quality. we show that focusing the analysis on text spans that the system identifies as being smell qualities makes the output more precise and tailored to the domain of interest. the results are validated on a selected set of smell sources from the benchmark, which is available at https://github.com/dhfbk/scent-change . ## related work there is limited research involving the diachronic analysis of sensory language, and the use of computational methods to study this phenomenon are even scarcer. among the few works investigating this research direction @xcite proposes an analysis of the possible variations of olfactory lexicon in the transition from latin to italian. the results of the study show that olfactory lexicon did not present substantial alterations in its overall size and differentiation. however, there is evidence suggesting that it did evolve towards a more negatively-oriented lexicon. in @xcite , the authors test the hypothesis of the directionality of sensory adjectives in latin and italian from a diachronic perspective. this study provides evidence for the fact that the primary meanings of sensory adjectives and the hierarchy of synaesthetic metaphors did not undergo variations over time. as regards the development of structured re-sources to investigate the evolution of sensory language, @xcite present a multilingual taxonomy for olfactory-related terms, which was created semi-automatically, with the goal to describe the evolution of odours and smell sources' descriptions. furthermore, in @xcite , the authors present a multilingual benchmark, manually annotated with smell-related information, to support the development of olfactory information extraction systems. nevertheless, the first exploratory analysis of shifts in olfactory descriptors based on word embeddings between two time periods is introduced in @xcite . the approach is inspired by the method for semantic change detection in el-ebshihy et al. @xcite , which was adapted to detect perception shifts rather than semantic ones. the hypothesis is that methods employed to detect how the meaning of a word changes over time (i.e. semantic shift) @xcite can be adapted to analyse possible variations in the way sensory items are perceived and therefore described over time (i.e. perception shifts). the work we present in this paper further investigates this phenomenon by introducing a novel benchmark to study olfactory perception shifts. we also present a comparison between a 'traditional' pmi-based approach to shift detection @xcite and our contribution that introduces an intermediate layer focusing on specific semantic roles. ## benchmark of smell perception shifts given the difficulty to evaluate shifts in language use, we first develop a benchmark with the purpose to trace the history of some selected odors over time. this resource can be used as a test set for the evaluation of systems analysing possible changes in the way specific odors have been described in the past. we rely on historical studies in the olfactory domain @xcite and on the online encyclopedia of smell history and heritage foot_0 to identify 16 words that domain experts consider particularly related to smell and whose perception may have changed over time: asphalt, candle, brewing, car, chloride of lime, coffee, (perfumed) gloves, incense/frankincense, lavender, ozone, pomander, plastic, sulphur, tea, tobacco, wig. for each of the above items, we then gather information on the perception shift it underwent, trying to address when this happened, whether it involved some changes in smell quality, whether it is connected to a change in location, and what type of shift it was. indeed, we identify four possible types of perception shift, manually checked by two experts in olfactory language: for each item in the benchmark, we specify one of the above types of perception shift, as well as the time period when the shift happened, the bibliographic or sitographic references, and in some cases the associated places for each period. note that for each term in the benchmark different time periods may be related to a perception shift. in ## olfactory information extraction our approach to analyse perception shifts in the olfactory domain relies on two components: i) a system for olfactory information extraction, and ii) a historical corpus of english, possibly wellbalanced across topics and time periods, which is processed with the above system. ## analysis of perception shifts in our analysis, we aim at detecting possible variations in the way specific smell-related concepts are described over time. for the sake of brevity, we focus our investigation on five smell sources selected from the benchmark (section 3) that undergo some sort of change in terms of perception over time: candle, gloves, incense/frankincense, ozone, tobacco. nevertheless, our approach to perception shift analysis can be generalised to any smell source. to conduct our study we use the corpus presented in section 4.2, which was processed with the system for olfactory information extraction (section 4.1). ## discussion our analyses provide insights into the olfactory changes that were identified by domain experts, validating them from a quantitative point of view. however, we observe some differences in the outcome of our analyses. the results which better reflect the shifts manually identified in our benchmark are those whose changes were labeled as quality shift, namely 'candle', 'ozone' and 'tobacco'. this is not surprising considering that we focus on text spans classified as quality. when it comes instead to'incense' and 'gloves', whose changes in perception are identified respectively as topic shift smell time period source incense (8,310) 1530 -1600 1601 -1800 1801 -1900 1901 -2000 aromatical perfume vernal dragge noisomely nidorous somnolent donative perfume odours breathe breezy frank sepulchred sacerdotal exasperate sweet perfumed acceptable perfumed sanguinary perfuming frank wafting fragrant fuming strange odours raptourous sweetsmelling sacred perfuming odoriferous burnt holy perfume murky lawny heavenly enrage candle (1,186) 1500 -1700 1701 -1829 1830 -1900 1901 -2000 abominable lighted ferous snuffing salutary guttering fragrance fumigating ill lighting offensive lighted corrupt arsenicated scented relighted fetid blinking ill cerifera filthy relighted nauseous lighting stink tallow odoriferous stationery snuff fumigating scent lighted odoriferous cereus olfactory suppurating unsavoury sputtering perfume flickering gloves (670) 1500 -1750 1751 -1900 1901 -2000 excellent perfumed perfume perfuming perfume gauntleted venomous fringed spanish pictured scented buttoning fine imbroidered remarkable cuticular scent boxing rich itchy costly worded odoriferous unbuttoning sweet scented excellent worshipful odorous rubber tobacco (7,516) 1600 -1730 1731 -1800 1801 -1900 1901 -2000 hateful smoaked olfactory smoky undiminished pipeful homely latakia fulsom nicotian perfume chewing hateful negrohead indefinable unmanufactured ungrateful fulling peculiar fulling superficial unmanufactured spirituous chewing offensive heroically grateful narcotick snug superexcellent stale carcinogenic bad spicery pungent chewed vilest smoaking medicinal snuffing ozone (830) 1840 -1899 1900 -1950 1951 -2000 restorative allotropique refresh ozonized photochemical inexhaustible oxidiser odorless allotropique none diurnal denser ozonized peculiar triatomic found antarctic electrical sterilizes fresh ultraviolet nickelic obvious vigorating pungent transboundary spheric and disappearance, the results are less evident compared to the defined changes in the benchmark. our findings suggest that different types of shifts may require distinct approaches for proper detection. indeed, if we want to capture shifts mostly due to disappearance, an analysis like the one displayed in figure 1 is probably more effective than the one based on pmi, in particular because we identify to what extent an item is considered a smell source, see for example the graph for 'gloves' after 1950. nevertheless, qualities associated with gloves in the olfactory analysis closely align with the way perfumed gloves were described during their historical use. adjectives such as 'venomous' or 'spanish' are indeed part of the practice to perfume gloves, since venom is hidden by the perfume and has been used to kill monarchs, while 'spanish' recalls the origin of glove-perfuming tradition from spain and italy. this observation provides further confirmation that this analytical approach effec-tively identifies qualities exclusively related to the olfactory domain with a precision that faithfully reflects the actual historical data. on the contrary, with regards to 'incense', its pronounced olfactory significance, as previously observed in section 5.1, presented a challenge in detecting noteworthy changes through the quality-based methodology. to uncover topic shifts in textual data, further research is needed. ## conclusions in this paper, we describe a range of analyses to investigate changes in the perceptual descriptions of five selected smell-related objects in textual data. we first present a frequency-based analysis aimed at delineating the olfactory relevance of these items over time. we then perform a pmi-based analysis to identify the qualities linked to smell sources during specific time periods, with the attempt to uncover changes in descriptions that reflect actual shifts in perception. additionally, we carry out a further analysis using pmi to represent the items of interest with vectors. the outcomes of these analyses support a twofold observation. on the one hand, the approaches previously used to detect diachronic semantic change prove effective in identifying variations also with regards to perceptual descriptions. on the other hand, the effectiveness of this adaptation is also due to the systematic encoding of the olfactory information offered by the frame-based approach. this work shows a novel approach which combines the power of frames in depicting semantic context and the tradition of semantic change detection to explore the evolution of olfactory language from a diachronic perspective. as previously discussed in section 6, it would be worthwhile to expand our investigations by employing alternative frame elements to identify topic shifts associated with specific smell objects. additionally, in the light of the observation made in section 5.3, extending also the embedding-based approach to this type of shift detection could represents a promising path for prospective research. in future, we plan to further develop this methodology aiming towards a comprehensive approach for the study of perceptual shifts in texts.