National Numeracy Network > Teaching Resources > Quantitative Writing > Examples > Quantifying gustatory sensitivity using signal detection theory

Quantifying gustatory sensitivity using signal detection theory

Julia Strand, Carleton College
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This material was originally developed as part of the Carleton College Teaching Activity Collection
through its collaboration with the SERC Pedagogic Service.

Summary

In this lab, students explore the complex relationship between sensory stimulus and perceptual experience. This lab demonstrates how "noise" in the perceptual system, individual variability, and sensory adaptation influence perceptual judgments. Students serve as both experimenters and subjects to collect psychophysical data on gustatory detection of sugar in water, and assess how these data change due to sensory adaptation when extremely sweet water is also tasted. Students explore individual differences in sensitivity (d') and criterion (Beta), represent their results visually using receiver operator characteristic (ROC) curves, and complete a group report describing their results, evaluating the methodology, and identifying possible real-world applications for signal detection theory.

Learning Goals

The goal of this project is to help students understand the complexity of the relationship between sensation and perception. In addition, they should become familiar with how psychophysical testing is conducted (including the complications of psychophysical measurement) and how signal detection theory informs perceptual research.

Context for Use

This assignment is most appropriate for a mid-level undergraduate psychology course in Sensation & Perception. The assignment requires data collection in pairs (1-2 hours), and computer time to analyze their results, create a figure, discuss the results with their group, and complete a group report with their findings (1 hour). Prior to beginning the activity, students should be exposed (through textbook or lecture) to background information on psychophysics and signal detection theory. The lecture or group report may be completed in a separate session from the psychophysical testing. Data collection requires water, sugar, small testing cups, plastic pipettes, and paper towels.

Description and Teaching Materials

The following steps provide an outline of the activity:
  • Instructor assigns relevant readings on signal detection theory including introducing the concepts of d', Beta, and ROC curves, and provides a brief lecture on the material.
  • Students are assigned to pairs and given a jug of plain water and jug of sugar water (approximately 4 tsp/gallon), along with small tasting cups and pipettes
  • Working in pairs, one student (the experimenter) gives "blind" samples via pipette to the taster in randomized order. The taster responds whether they detect the flavor (is there sugar in the water?) and the experimenter records the response as a hit, miss, false alarm, or correct rejection. Students take turns in the roles of experimenter and taster.
  • After both students have served both roles, the process is repeated, but the second time, the students intersperse sips of very sweet water (1 cup/gallon).
  • For both team members in both conditions, students calculate the probability of hits, misses, false alarms, and correct rejections. From these, they calculate d' values (indicating perceptual sensitivity).
  • Students create ROC curves representing their results, and complete a group report detailing their findings.

Instructions for data collection (Microsoft Word 2007 (.docx) 98kB Sep17 12)

Group report (Microsoft Word 2007 (.docx) 68kB Sep17 12)

Teaching Notes and Tips

In a later Sensation & Perception lab, we will conduct tongue-staining in order to determine the density of fungiform papillae on each student's tongue, and measure their taste sensitivity using PROP tasting strips. The data from this signal detection lab may be used to correlate individual differences in d' with individual differences in papillae density and PROP bitterness ratings.

This lab could also easily be adapted to auditory perception. In that case, students could be presented with files containing no sound and files containing a very quiet tone. Adaptation could be achieved by completing testing after being in a quiet room vs. a noisy classroom.

Assessment

In the group report, students are asked to include methodological concerns that may have influenced testing. This is an opportunity to assess their knowledge of experimental control and potential confounds (e.g., having recently eaten or not rinsing the pipettes between uses). They are also asked to speculate about why responses are inconsistent and what factors (other than the presence of absence of a stimulus) influences responses.

References and Resources