Abstract
Odorants exert their effects at many levels. Most often, these stimuli are well above detection threshold and allow the investigator to use self-report or behavioral techniques to evaluate odor effects. There are, however, considerable data demonstrating effects for odor stimuli that are below sensory thresholds or are undetected by subjects. In these cases, self-report is of little use, and brain imaging has been very effective in helping to explain these findings. This paper reviews the problem of low-intensity odors and the application of a wide variety of brain imaging techniques to research on this phenomenon. Finally, a model of undetected odor effects and brain imaging is presented to help simplify the variations in nomenclature that are used to describe this field.
Similar content being viewed by others
References
Bargh JA, Morsella E (2008) The unconscious mind. Perspect Psychol Sci: J Assoc Psychol Sci 3(1):73–79
Black SL, Smith DG (1994) Has odor conditioning been demonstrated? A critique of “unconscious odour conditioning in human subjects. Biol Psychol 37:265–267
Block N (1995) On a confusion about a function of consciousness. Behav Brain Sci 18:227–287
Block N (2007) Consciousness, accessibility, and the mesh between psychology and neuroscience. Behav Brain Sci 30(5–6):481–499
Brefczynski JA, DeYoe EA (1999) A physiological correlate of the ‘spotlight’ of visual attention. Nat Neurosci 2:370–374
Dehaene S, Changeux J-P, Naccache L, Sackur J, Sergent C (2006) Conscious, preconscious, and subliminal processing: a testable taxonomy. TRENDS Cogn Sci 10:204–211
Dennett D (1991) Consciousness explained. Little, Brown & Co., Boston
Duncan J (1981) Directing attention in the visual field. Percept Psychophys 30:90–93
Engen T (1982) The perception of odors. Academic Press, New York
Gazzaniga MS (1998) Brain and conscious experience. Adv Neurol 77:181–192
Grabenhorst F, Rolls ET, Margot C (2011) A hedonically complex odor mixture produces an attentional capture effect in the brain. NeuroImage 15:823–843
Green DM, Swets JA (1966) Signal detection theory and psychophysics. Wiley, New York
Hansen JC, Hillyard SA (1983) Endogenous brain potentials associated with selective auditory attention. Electroencephalogr Clin Neurophysiol 49:277–290
Hummel T, Mojet J, Kobal G (2006) Electro-olfactograms are present when odorous stimuli have not been perceived. Neurosci Lett 397(3):224–228
Jacob S, Kinnunen LH, Metz J, Cooper M, McClintock MK (2001) Sustained human chemosignal unconsciously alters brain function. Neuroreport 12:2391–2394
Jacquot L, Monnin J, Brand G (2004) Unconscious odor detection could not be due to odor itself. Brain Res 1002(1–2):51–54
Kail R (1997) The neural noise hypothesis: evidence from processing speed in adults with multiple sclerosis. Aging Neuropsychol Cogn 4:157–165
Kirk-Smith M, Van Toller C, Dodd G (1983) Unconscious odour conditioning in human subjects. Biol Psychol 17:221–231
Kline J, Schwartz GE, Kikman ZV, Bell IR (2000) Electroencephalographic registration of low concentrations of isoamyl acetate. Conscious Cogn 9(1):50–65
Koch C, Tsuchiya N (2006) Attention and consciousness: two distinct brain processes. Trends Cogn Sci 11:16–22
Koivisto M, Kainulainen P, Revonsuo A (2009) The relationship between awareness and attention: evidence from ERP responses. Neuropsychologia 47:2891–2899
LaBerge D (1983) Spatial extent of attention to letters and words. J Exp Psychol: Hum Percept Perform 9(3):371–379
Li W, Lopez L, Osher, Howard J, Parrish T, Gottfried J (2010) Right orbitofrontal cortex mediates conscious olfactory perception. Psychol Sci 21:1454–1463
Libet B (1991) Conscious vs. neural time. Nature 352:27–28
Lorig TS (1989) Human EEG and odor response. Prog Neurobiol 33:387–398
Lorig TS (1999) On the similarity of odor and language processing. Neurosci Biobehav Rev 23:391–398
Lorig TS, Schwartz GE (1988) Brain and odor I: alteration of human EEG by odor administration. Psychobiology 16:281–284
Lorig TS, Herman KB, Schwartz GE, Cain WS (1990) EEG activity during administration of low concentration odors. Bull Psychon Soc 28:405–408
Lorig T, Huffman E, DeMartino A, DeMarco J (1991) The effects of low concentration odors on EEG activity and behavior. J Psychophysiol 5(1):69–77
McClintock MK (1971) Menstrual synchrony and suppression. Nature 229:244–245
McClintock MK (2002) Pheromones, odors and vasnas: the neuroendocrinology of social chemosignals in humans and animals. In: Pfaff DW et al (eds) Hormones, brain, and behavior, vol 1. Academic Press, New York, pp 797–870
Merikle PM, Daneman M (2000) Conscious vs. unconscious perception. In: Gazzaniga MS (ed) The new cognitive neurosciences, 2nd edn. MIT Press, Cambridge
Moore T (2006) The neurobiology of visual attention: finding sources. Curr Opin Neurobiol 16(2):159–165
Pause BM, Krauel K (2000) Chemosensory event-related potentials (CSERP) as a key to the psychology of odors. Int J Psychophysiol 36:105–122
Plailly J, Howard JD, Gitelman DR, Gottfried JA (2008) Attention to odor modulates thalamocortical connectivity in the human brain. J Neurosci 28:5257–5267
Schwartz GE, Bell IR, Dikman ZV, Fernandez M, Kline JP, Wright KP (1994) EEG responses to low-level chemicals in normal and cacosmics. Toxicol Ind Heal 10:633–643
Sela L, Sobel N (2010) Human olfaction: a constant state of change-blindness. Exp Brain Res 205(1):13–29
Shepherd GM (2004) The human sense of smell: are we better than we think? PLoS Biol 2(5):e146, Public Library of Science
Sobel N, Prabhakaran V, Hartley C, Desmond J, Glover G, Sullivan E, Gabrieli J (1999) Blind smell: brain activation induced by an undetected air-borne chemical. Brain: J Neurol 122(2):209
Sommer W, Matt J (1990) Awareness of P300-related cognitive processes: a signal detection approach. Psychophysiology 27:575–585
Spence C, Driver J (1997) On measuring selective attention to an expected sensory modality. Atten Percept Psychophys 59:389–403
Stevenson RJ (2009) Phenomenal and access consciousness in olfaction. Conscious Cogn 18(4):1004–1017
Veldhuizen MG, Small DM (2011) Modality-specific neural effects of selective attention to taste and odor. Chem Senses 36:747–760
Walla P, Hufnagl B, Lehrner J, Mayer D, Lindeinger G, Deecke L, Lang W (2002) Evidence of conscious and subconscious olfactory information processing during word encoding: a magnetoencephalographic study. Cogn Brain Res 14:309–316
Zelano C, Bensafi M, Porter J, Mainland J, Johnson B, Bremner E, Telles C et al (2004) Attentional modulation in human primary olfactory cortex. Nat Neurosci 8(1):114–120
Zucco GM, Paolini M, Schaal B (2009) Unconscious odour conditioning 25 years later: revisiting and extending “Kirk-Smith, Van Toller and Dodd. Learn Motiv 40(4):364–375
Acknowledgement
The author is indebted to W. Whiting, D. Small, S. Warrenburg, B. Lorig, and an anonymous reviewer for their suggestions and comments on this manuscript.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Lorig, T.S. Beyond Self-report: Brain Imaging at the Threshold of Odor Perception. Chem. Percept. 5, 46–54 (2012). https://doi.org/10.1007/s12078-012-9116-x
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12078-012-9116-x