binding sites that are low or high afﬁnity, and as the concen-
tration of a compound increases the lower afﬁnity receptor
or active site of the receptor is activated (Galindo-Cuspinera
et al. 2006).
Within an individual, the strength of an afferent signal may
be magniﬁed relative to other individuals. There may also be
interindividual variations in the signal processing in the
human brain, although our understanding of gustatory pro-
cessing in the brain is still in its infancy (Small 2006).
There is a complex relationship between chemical concentra -
tion, detection threshold, and suprathreshold intensity of
bitter compounds. The sensitivity of a person to detect very
low concentrations of a compound is not necessarily associ -
ated with their sensi tivity to the same compound when it is
perceivably bitter. Moreover, in some situations, threshold
sensitivity to a compound may be inversely related to the in-
tensity of perceived bitterness of that compound. Such com-
plexity has practical implications as threshold determination
methods are increasingly (and incorr ectly) used to infer
suprathreshold intensity of speciﬁc compounds, for example,
taste dilution analysis, (Frank et al. 2001; Ottinger et al.
2003). More broadly, this paper also continues to support
that attempts to link threshold measures to food sensations
and intake are at best misguided.
The bitter taste system may have distinct perceptual stages,
one for threshold and at least one for suprathreshold inten-
sities, and these perceptual stages may relate to distinct oral
peripheral mechanisms. As the concentration of a compound
increases, receptors that have a lower afﬁnity for the com-
pound may become involved in the process of taste transduc-
tion, resulting in perceptual phases that can be differentiated
using psychophysical methods of evaluat ion.
We thank Professor Sing Kai Lo for his advice on the statistics
undertaken in this study. Financial support was received from
the School of Exercise and Nutrition Science, Deakin University.
We thank all the subjects who took part in this study.
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