Temporal Characteristics of Human Taste Judgements as Calibrations for Gustatory Event-related Potentials and Gustatory Magnetoencephalographs

Abstract

Activity in the central nervous system (CNS) constantly fluctuates. CNS changes that are potential responses to sensory stimulation must occur before an observable external outcome of the stimulation. If the external change is an overt, measurable behavior, then the time interval between a controlled stimulus and the behavior is a reaction time (RT) (Halpern, 1986, 1991, 1994). Human RT can be used to predict when relevant changes in human CNS activity in response to a specified controlled stimulus will occur. Therefore, human RT both indicate the time after stimulus onset (latency) when relevant human CNS changes should be found and provide a means of excluding CNS changes for which the latency is too long. Human gustatory RT require controlled stimuli with known arrival times, concentration profiles and durations. They can be provided by rapidly changing from a carrier liquid (solvent only) to a stimulus liquid (solvent plus solute), both delivered at a fixed flow rate and temperature over a consistent and limited area of the human tongue for predetermined durations and then rapidly changing back to the carrier liquid (e.g. Kelling and Halpern, 1983, 1987, 1988). Physical measurements at the tongue of concentration changes over time provide calibration of stimulus duration and concentration profile. Effects of the rapid change events on RT are identified by ‘changing’ from carrier liquid to carrier liquid, thus controlling for responses to alterations in liquid flow. If subjects are asked to respond only to taste changes and are given identified practice trials during which there is, or is not, a change from carrier liquid to stimulus liquid and back to carrier liquid, then reports of a change in taste during unidentified simple taste reaction time (RTs) control trials average 100 ms (Kelling and Halpern, 1987). RT responses may require movement of a button or lever, or a spoken word; in some instances, a computer display gives feedback. All timing accuracy can be at the millisecond level.