Rating a New Hedonic Scale: A Commentary on "Derivation and Evaluation of a Labeled Hedonic Scale" by Lim, Wood and Green

Abstract

To the extent that our experiences of tastes and odors haveunderlyingdimensions, onecanmountastrongcase thattheexpression of those dimensions is via hedonics (Scott andMark1987;Khanetal.2007).Thehedonicdimensioniscru-cialin defining responses in the chemical senses in awaythatis not true for other senses, in that all chemosensory stimuliare intrinsically valenced, either at birth (e.g., in the case ofsweetness and bitterness) or as a result of our subsequent ex-perienceswiththem(arguablythecaseforallodorqualities).Traditional psychophysics, developed primarily for studiesin vision, audition or touch, asks questions about stimulusintensity, but this may be of less importance for taste orsmell, which derive much of their meaning from theirhedonic properties. Moreover, certainly in the case of tastequalities, our hedonic responses may provide crucial cluesregarding the adaptive significance of those qualities. Assuch, the overall paucity of attempts to ‘‘fine tune’’ our psy-chophysical methods in relation to chemosensory hedonicsis all the more puzzling.Even in the tortoise world of psychophysics, the develop-mentofhedonicmeasurementhasbeenstartlinglyslow.Thismay be because much of the interest in psychophysical mea-surement has been centered on addressing the question ofhow best to directly access perceptual processes, that is, tocharacterize sensory systems in psychological terms, whichcouldthenbeusefullylinkedtounderlyingphysiologicalpro-cesses. The importance of the development of the LabeledMagnitude Scale (LMS), first published in 1993 (Green et al.1993), and later modified as the general (g)LMS (Bartoshuket al. 2002), lies in the attempt to provide a means of scalingconsistent with S.S. Steven’s psychophysical model, whichspecified a relationship between physical stimulus magni-tude and sensation in ratio terms. Magnitude estimation(ME), derived from the same theoretical base, enjoyed a pe-riod of application that has waned in recent decades. It hasbeen suggested that the primary reasons for ME falling outof favor was both that people do not themselves consis-tently use numbers in a ratio fashion and also that the mea-surement process itself was unwieldy because of the priortraining that was deemed necessary. Thus, the introductionof the LMS was timely, quickly being adopted by manypsychophysical researchers, especially those hoping fora measurement free of the context of the stimuli under mea-surement (Bartoshuk 2000).Accessing ‘‘secondary states,’’ including the hedonic eval-uationofsensorystimuli,hasbeenregardedaslessimportantbecauseithasbeenfeltthatthestimulus-affectiverelationshipis less direct (although there is evidence that affective statesmight occur in the absence of perceptual awareness—seeKunst-Wilson and Zajonc 1980), has less to tell us aboutperception per se, and is further from being ‘‘objective,’’ inthataffectivestatesclearlyshowconsiderableindividualvar-iability(often,oforiginunknown).Ironically,todate,oneofthemostcommon applicationsofthe gLMShasbeeninthestudyofindividualdifferencesinperception,particularlyinrelationtooralirritationand6-n-propylthiouracilbitterness(Bartoshuk 2000; Prescott et al. 2001; Green and Hayes2003). One of the benefits of the gLMS is that, via the useofasupposed(andperhaps,inpractice,actual)frameofref-erence external to the stimuli themselves, generated by thetop-end label ‘‘Strongest Imaginable Sensation of AnyKind,’’wecanminimizethegenerallyuninterestingvariabil-ityassociatedwithscaleusageandmaximizethequiteinter-esting variability associated with individual perceptual orphysiological differences. Affective states and responsesare, of course, expected to show considerable individual