Students need practice in proposing hypotheses, developing experiments that will test these hypotheses, and generating data that they will analyze to support or refute them. I describe a guided-inquiry activity based on the “tongue map” concept, appropriate for middle school and high school students.

In 1901, German scientist D. P. Hänig published a paper describing the relative taste sensitivities of different parts of the human tongue, testing sweet, salty, bitter, and sour (Hänig, 1901). He reported that each section of the tongue was able to taste all flavors, but that there were small differences in threshold sensitivities between volunteers.

Hänig’s data were reinterpreted in a 1942 book, Sensation and Perception in the History of Experimental Psychology (Boring, 1942), and presented in a way that made people think that each section of the tongue had large differences in its ability to taste flavors. Boring published this figure in the book (Figure 1):

Figure 1.

Distribution of taste sensitivity along the edge of the tongue (Boring, 1942, p. 452).

Figure 1.

Distribution of taste sensitivity along the edge of the tongue (Boring, 1942, p. 452).

And similar figures have often appeared in books since, such as this (Figure 2):

Figure 2.

Drawing of taste sensitivity on the human tongue. “Approximate location on the tongue of regions of greatest taste sensitivities for the four primary taste qualities. For the bitter taste, the soft palate (not shown) is the most sensitive region” (Schiffman, 1995).

Figure 2.

Drawing of taste sensitivity on the human tongue. “Approximate location on the tongue of regions of greatest taste sensitivities for the four primary taste qualities. For the bitter taste, the soft palate (not shown) is the most sensitive region” (Schiffman, 1995).

Somehow this information became mutated over time, and people believed that each section of the tongue could taste only one flavor. This became known as the “tongue map,” represented by a figure like this one (Figure 3):

Figure 3.

A tongue map, similar to ones found in textbooks and on the Web, indicating that each section of the tongue can taste only one flavor.

Figure 3.

A tongue map, similar to ones found in textbooks and on the Web, indicating that each section of the tongue can taste only one flavor.

In 1974, Virginia Collings reanalyzed Hänig’s original research and performed her own experiments (Collings, 1974). She demonstrated that all parts of the tongue could sense all tastes, but with differing thresholds for the stimuli (Figure 4):

Figure 4.

Log taste thresholds of four tongue loci and the soft palate for urea, sodium chloride, sucrose, citric acid, and quinine hydrochloride. The horizontal lines indicate ±SE. Quinine is bitter, sucrose is table sugar, citric acid is vitamin C (sour), and urea tastes like ammonia. The y-axis indicates the lowest concentration (threshold) that subjects were able to taste.

Figure 4.

Log taste thresholds of four tongue loci and the soft palate for urea, sodium chloride, sucrose, citric acid, and quinine hydrochloride. The horizontal lines indicate ±SE. Quinine is bitter, sucrose is table sugar, citric acid is vitamin C (sour), and urea tastes like ammonia. The y-axis indicates the lowest concentration (threshold) that subjects were able to taste.

Further work has confirmed the hypothesis that all parts of the tongue can taste all flavors and has extended our knowledge of taste. For example, Linda Buck and colleagues later cloned the genes for some types of taste receptors and showed that these receptors are present in all taste buds (Matsunami et al., 2000), further debunking the myth of the tongue map. A fifth taste was identified, umami (glutamate, a savory taste found in high levels in many foods, including tomatoes and fish, sometimes described as a brothy or meaty taste; Chaudhari & Roper, 1998), and much work has been done to tease out the relative contributions of taste and smell to the overall sensation and pleasure of eating (Smutzer et al., 2006).

Activity

Many biology textbooks and books that cover classroom lab activities and science fairs, as well as online activities, still feature “maps” showing where each taste can be detected on the tongue (e.g., Wiese, 2000). There are also dozens of articles explaining that this tongue map is a misconception perpetuated through poor understanding of human physiology (e.g., http://www.livescience.com/7113-tongue-map-tasteless-myth-debunked.html).

Human gustation is a complex physiological process that only recently has begun to be unraveled (Smutzer et al., 2006). In the following guided-inquiry lab, students design and carry out their own experiment to support or refute the idea of tongue mapping. The purpose of the activity is not for the students to come to the “right” answer, because human taste physiology varies, but for the students themselves to design and perform experiments without a “cookbook” to guide them.

Students were given an overview of human taste and some of the experiments done to study taste, and a discussion of umami. They were then challenged to develop an experiment to support or refute the 1942 tongue map hypothesis (sweet, sour, bitter, and salty only; Figure 3), using their group as subjects and some or all of the items we supplied.

Materials

  1. Lemon slices (sour)

  2. Sugar

  3. Salt

  4. Instant coffee (bitter)

  5. Raw potato (no flavor), control or not used

  6. Jalapeño lollipops (capsaicin)

  7. Tomato paste (umami)

  8. Chicken broth (umami)

  9. Water (no flavor), control, used to cleanse palate, or not used

  10. Q-tips

  11. Toothpicks

  12. Spoons

Procedures

Students were told to design, conduct, and report the results of an experiment supporting or refuting the tongue mapping hypothesis, as reported in 1942, using sweet, salty, bitter, and sour tastes. They were told that their subjects would be the members of their team. We asked them to design an experiment that resulted in both qualitative and quantitative data that could be placed in a table, graphed, and analyzed via statistical methods. Students were expected to report on

  1. Statement of the problem (experimental question)

  2. Hypothesis and rationale

  3. Variables and their operational definitions

    • Independent variable

    • Dependent variable

    • Controlled variables

  4. Experimental control/control group

  5. Materials used and rationale for use (use only as many spaces as needed; you may not need all the items given)

  6. Procedure, including diagrams (if applicable)

  7. Qualitative observations

  8. Data table(s) (required)

    “Design a table to present your data. Ensure that your table is complete, with raw data, units, labels, calculations (if appropriate), and significant figures (if appropriate). Indicate how many trials and how many subjects.”

  9. Statistics

  10. Analysis and interpretation of data

  11. Possible experimental errors

  12. Conclusion

  13. Applications and recommendations for further use

The rubric we used to assess the activity was modified from the Science Olympiad rubric:

  1. Statement of problem (4 points)

    _____ Not a yes/no question

    _____ Independent and dependent variables included

    _____ Problem clearly testable

    _____ Response written in a clear and concise manner

  2. Hypothesis (4 points)

    _____ Statement predicts a relationship or trend

    _____ Statement gives specific direction to the predictions(s): A stand is taken

    _____ Prediction includes both independent and dependent variables

    _____ A rationale given for the hypothesis

  3. Variables

    Independent variable (IV) (3 Points)

    _____ IV correctly identified

    _____ IV operationally defined

    _____ At least three levels of IV given

    Dependent variable (DV) (3 points)

    _____ (2) DV correctly identified

    _____ DV operationally defined

    Controlled variables (CV) (4 points)

    _____ One CV correctly identified

    _____ Two CVs correctly identified

    _____ Three CVs correctly identified

    _____ Four CVs correctly identified

  4. Experimental control (3 points)

    _____ Control(s) correctly identified

    _____ The control(s) makes logical sense for the experiment

    _____ Reason given for selection of control(s)

  5. Materials (3 points)

    _____ All materials used are listed

    _____ All materials used are listed properly (no extras)

    _____ Materials are listed separately from procedure

  6. Procedure, including diagrams (6 points)

    _____ Procedure well organized

    _____ Procedure is in a logical sequence

    _____ (2) Enough information given so that another could repeat procedure

    _____ Diagrams used

    _____ Repeated trials

  7. Qualitative observations (4 points)

    _____ Observations about results given

    _____ Observations about procedure/deviations given

    _____ Observations about results not directly related to DV

    _____ Observations given throughout the course of the experiment

  8. Quantitative data – data table (6 points)

    _____ All raw data given

    _____ All data have units

    _____ Condensed table with most important data included

    _____ Table(s) labeled properly

    _____ Example calculations given

    _____ All data reported using correct significant figures

  9. Graph(s) (6 points)

    _____ Appropriate type of graph used

    _____ Graph has title

    _____ (2) Graph labeled properly (axes/series)

    _____ Units included

    _____ Appropriate scale used

  10. Statistics (6 points)

    _____ (3) Mean, median, or mode

    _____ Measure of variation

    _____ Regression analysis

    _____ Other appropriate statistic used

  11. Analysis and interpretation of data (4 points)

    (All statements must be supported by the data)

    _____ All data discussed and interpreted

    _____ Unusual data points commented on

    _____ Trends in data explained and interpreted

    _____ Enough detail given to understand data

  12. Possible experimental errors (3 points)

    _____ Possible reasons for errors given

    _____ Important info about data collection given

    _____ Effect errors had on data discussed

  13. Conclusion (4 points)

    _____ Hypothesis evaluated according to data

    _____ Hypothesis restated

    _____ Reasons to accept/reject hypothesis given

    _____ All statements supported by the data

  14. Applications and recommendations for further use (4 points)

    _____ Suggestions for improvement of specific experiment given

    _____ Suggestion for other ways to look at hypothesis given

    _____ Suggestions for future experiments given

    _____ Practical application(s) of experiment given

Results

We purposefully gave students more items than they would need (such as the lollipops and umami tastes), just as a real scientist has more chemicals available to her in the lab than she would use for any individual experiment. Part of the activity is to design an experiment that tests the hypothesis; thus, giving the students only the items they need defeats the purpose of the activity, which is student-designed research. An alternative approach would be to give the class the experimental question and have them determine a shopping list as well.

I used this activity for an Experimental Design Section of the Arizona Science Olympiad. Students were given 50 minutes to propose a hypothesis and then to develop, execute, and analyze their own experiment based on their hypothesis. They had to develop a quantitative method to score taste and were challenged to graph their results. Because 50 minutes was a very short amount of time for the activity and for classrooms, I suggest 2 hours at least, broken up into developing the hypothesis and designing the experiments, and then performing the experiment and analyzing the data.

This particular experiment was especially well suited for guided inquiry at many levels because the items are relatively inexpensive, students love to study themselves and the human body, and developing a method and determining which foods to use is not as simple as one might think. Eighteen of the groups we challenged (31 groups competing in the Arizona Science Olympiad) did not choose the correct variables to test the hypothesis. Other groups were not sure how to quantify the results or how to analyze their results in light of the hypothesis they developed.

Fourteen groups’ experimentation supported the tongue map hypothesis. Some students reported that different parts of their tongue had strong variation in taste sensitivities, and others reported no differences at all. Thus, there is individual-to-individual variation in the threshold response on different parts of the tongue. In this experimental setup, not everyone is going to obtain the same results, even if the same trials are run on them, and so every individual or group can propose and test their own hypothesis, and then students as a whole can come together in class to discuss differences and then analyze the group data, perhaps even controlling for variables such as age and favorite foods.

Turning the ubiquitous tongue map activity into a guided-inquiry lab helps students develop and propose hypotheses as well as design and carry out their own series of experiments. This activity fits the guidelines of “Understanding about the Nature of Science” of the Next Generation Science Standards (http://www.nextgen.org) and is applicable at all grades, depending on the amount of instructor input.

Acknowledgments

I thank Drs. Kimberly Curlee and Bronwen Steel for proofreading the student handout and assistance at the Science Olympiad, and Lorenzo Sanchez for help at the Science Olympiad.

References

References
Boring, E. (1942). Sensation and Perception in the History of Experimental Psychology. New York, NY: Academic Press.
Chaudhari, N. & Roper, S.D. (1998). Molecular and physiological evidence for glutamate (umami) taste transduction via a G protein-coupled receptor. Annals of the New York Academy of Sciences, 855, 398–406.
Collings, V.B. (1974). Human taste response as a function of locus of stimulation on the tongue and soft palate. Perception & Psychophysics, 16, 169–174.
Hänig, D.P. (1901). Zur Psychophysik des Geschmacksinnes. Philosophische Studien, 17, 576–623.
Matsunami, H., Montmayeur, J.-P. & Buck, L. (2000). A family of candidate taste receptors in human and mouse. Nature, 404, 601–604.
Schiffman, H.R. (1995). The skin, body and chemical senses. In R.L. Gregory & A.M. Colman (Eds.), Sensation and Perception (p. 88). London, UK: Longman.
Smutzer, G., Sayed, S. & Sayed, N. (2006). Examination of human chemosensory function. American Biology Teacher, 68, 269–274.
Wiese, J. (2000). Head to Toe Science: Over 40 Eye-Popping, Spine-Tingling, Heart-Pounding Activities That Teach Kids about the Human Body. San Francisco, CA: Jossey-Bass.