HERTZ, MATHILDE CARMEN

(b. Bonn, Germany, 14 January 1891; d. Cambridge, United Kingdom, 20 November 1975), Gestalt psychology, comparative psychology, sensory physiology.

Hertz was a pioneering comparative psychologist. She fused psychological and biological perspectives in her research, and contemporary psychologists and biologists alike held her work in high esteem. She combined innovative experimental techniques and Gestalt principles to examine the visual perception of diverse animal species, including ravens, honeybees, butterflies, and hermit crabs. Time and again facing adversity, Hertz overcame various obstacles to pursue an academic career. She was prolific while her career lasted, but her scholarly work ended abruptly after she emigrated from Germany to England in 1936.

Short Biography . Mathilde Hertz was the youngest daughter of the physicist Heinrich Hertz, who died when Mathilde was three years old. After completing a nonclassical secondary education she began a career as a sculptor. To supplement her income she took a job at the library of the German Museum in Munich, where she drew and sculpted plastic reconstructions of fossilized teeth in the zoological collection. At this time her work came to the attention of Ludwig Döderlein, who was the director of the zoological collection. Overcoming barriers for a scientific career for women at that time, Hertz enrolled at the University of Munich from 1921 to 1922 and later completed her doctoral degree in 1925 with honors on a study about early mammalian jawbones under the supervision of Richard von Hertwig.

By 1925, and inspired by Wolfgang Köhler’s research with anthropoid apes, Hertz began work in the field of animal psychology. In 1927 she moved to Berlin and worked in the Department for Genetics and Biology of Animals under the auspices of Richard Goldschmidt. Here she taught and conducted research until her authorization to teach was withdrawn in 1933 due to the implementation of the “Law for the Restoration of Professional Civil Service.” According to this law, civil servants who were not of “Aryan descent” were to be retired, and those whose political stance did not guarantee loyalty to the Nazi regime to be dismissed. Hertz was presumably classified as “non-Aryan” according to this law because she had

one grandparent, Gustav Ferdinand Hertz, who had been Jewish prior to converting to Christianity.

Despite the intervention efforts of Max Planck, the president of the Kaiser Wilhelm Society at that time, she was no longer able to teach, although she continued her research until the end of 1935. Between 1925 and 1935 she published more than thirty articles. In 1936 Hertz immigrated to England, where, after publishing another article on color vision in bees (1939) and an article on vision in migratory locusts (1937b), her empirical work basically came to an abrupt end presumably due to an unfortunate combination of personal and professional factors. Various reasons for this are explored by Regina Siegfried Kressley-Mba and Jaeger (2003), including the fact that Hertz appears to have remained loyal to Germany despite the grave injustices she suffered as a result of Nazi racial policies. Furthermore, the growing popularity of ethology and an emphasis on instinctive behavior may have rendered the phenomenological orientation that was characteristic of Gestalt psychology and Hertz’s work obsolete.

Problem-Solving Behavior in Animals . Hertz’s first experiments with ravens were explicitly designed and implemented to examine the Gestalt laws of visual perception outlined by Max Wertheimer (1923; Hertz, 1928a, b). Although Gestalt theory offered the theoretical foundation for explaining organization in human perception, thinking, and behavior, Wertheimer viewed Hertz’s work as providing indispensable empirical evidence for Gestalt principles of visual perception among animals. Despite their significance for verifying those principles, Hertz’s experiments with ravens were valued in yet another light by Gestalt psychologists and zoologists alike, namely as central examples of problem-solving behavior in animals (Duncker, 1945). The methods employed by Hertz with ravens were later implemented in studies examining the problem-solving capacities of primates, for example, by the Gestalt psychologist and Köhler student Johannes von Allesch and the Dutch ethologist Johan Abraham Bierens de Haan.

In her experiments on the visual perception of ravens, Hertz altered the location of food rewards within identical configurations so that she was able to determine, among other things, how jays distinguish between concave and convex stimuli. Based on the assumption that ravens have only a weak sense of smell and that there is no trace of food originating from the hidden object, Hertz reasoned that the birds depend on memory and sensory input to locate the critical area and retrieve bounty by removing debris hiding the food (Hertz, 1928a, b). Based on similar experiments that Köhler had employed with anthropoids, Hertz hid a peanut or hazelnut while the bird was watching and then observed the bird’s behavior. This was Hertz’s solution for inducing the bird in a laboratory setting to engage in searching behavior that was not necessary for its survival (Hertz, 1928a). Initially the food was covered with a flowerpot as the birds watched. After the birds had learned this exercise, the goal objects and obstacles were modified to match the bird’s natural environment, such as using stones, wood, or grass. Hertz (1928a, b) implemented a countless variety of stimulus constellations to detect which variables were essential for finding the hidden food. Figure 1 provides an example of how Hertz tracked flight patterns. In order to rule out the possibility that the birds were responding on the basis of conditioning, Hertz incorporated critical trials in which both the target (food) and intermediate target (object hiding the food) were absent during the search phase.

Significant Findings in Animal Visual Perception . Hertz’s findings on visual perception in honeybees—cited by Karl von Frisch (1937)—probably represent her most significant contribution to animal sensory perception. Initially, Hertz worked with birds because their visual systems were similar to those of anthropoids, but later opted for honeybees because of their more primitive visual system. Her research with honeybees served as the basis for her postdoctoral thesis, for which Köhler served as one of the committee members.

Prior to Hertz’s work, von Frisch had concluded that bees cannot distinguish between basic geometric forms. Hertz modified von Frisch’s method by eliminating the conditioning of the bees prior to the experiments. Hertz (1931) covered a table with black and white figures varying in form and degree of contour and placed bowls of sugar water between the forms. She then observed flight patterns relative to the forms—namely, which sources of food next to which form were frequented by the most bees, most quickly, and most often. Realizing that conditioning to a particular stimulus occurs automatically through preferences developed over the course of a few trials, Hertz then attempted to condition the bees to a different form. The relative resistance of conditioning to a particular stimulus was a further measure of the kind and degree of spontaneous response (Hertz, 1935a).

If bees could not distinguish between triangles and squares as von Frisch had observed, then it was because

they preferred shapes full of contour, which was supported by independent findings that bees could distinguish flowers. Hertz was able to determine visual preferences in bees with regard to patterns (see Figure 2). She coined the term figural intensity to designate the visual quality of a figure— the more differentiated and the more pronounced the contours, the greater the bees’ preference for those figures. Figural quality referred to the basic type of figure (i.e., circle versus star). Hertz (1931) also used variations of forms and patterns to test bees’ perception of depth, contrast, and patterns as well as presenting the stimuli at different times of day to study light and shadow effects, particularly during flight approaching a stimulus. These were experimental variations originating from Hertz’s earlier work with ravens.

A Compelling Fusion of Biology and Psychology . Hertz’s work on the visual perception of ravens exemplifies her conceptual and methodological orientation. Hertz (1928a) had determined that birds picked an object under which the reward was hidden based on the degree of convexity of the object and not on other visual cues in its surroundings. The fact that convexity was an essential visual cue seemed to be consistent with factors in their natural behavioral repertoire, such as jumping or flying from branch to branch and their capacity for depth perception. Hertz’s consideration of animals’ behaviors in their natural habitats distinguished her from her mentor Köhler.

In a departure from other psychologists working in the field of animal psychology at that time, Hertz did not discount the role of instinct in helping shape behavior. In an essay originally published in French in 1937, Hertz elaborated on the relationship between instinct and intelligence in the animal kingdom. Because the essay appeared so late in her professional career, it reflects the culmination of her views regarding animal behavior in light of her research up to that point in time. She pointed out in the essay that instinct and intelligence were originally thought to be mutually exclusive, but new reports about intelligent behavior in animals had led to questions regarding the relationship between the two (Hertz, 1937a). In this respect, Hertz differed from Köhler in refusing to discount the role of instinct in animal behavior and in her insistence on the “inevitability of the concept of instinct in biology” (Jaeger, 1996, p. 240).

However, contrary to biologists who totally denounced the use of analogy in animal psychology research, Hertz (1933) claimed that although humans and bees have a totally different visual perception of their environment, statements about the perception of experimental animals can be made only by assuming certain fundamental similarities in perceptual processes. Based on this assumption, experiments can be designed to either support or negate the validity of such analogies. By determining the limitations in experimental animals we gain knowledge about the effectiveness of other organisms in comparison with ourselves. Perhaps for this reason she stated dogmatically and unequivocally that, “No sensory physiology is feasible, that would not sooner or later be comparative psychology and nothing but this” (1933, p. 12). Hertz was referring to the fact that both explicit and implicit inter-species comparisons are inevitable in sensory physiology. The defensive tone of Hertz’s statement underlines the precarious position of comparative psychologists within animal research at that time and Hertz’s identification of herself as a comparative psychologist.

Hertz (1933) stated the imperative for comparative psychology in her article on figural intensities and qualities in the optical perception of bees. Although a stimulus is defined or interpreted as an external event causing changes in behavior, there is the temptation to quickly infer that one particular stimulus elicits a reaction. Hertz pointed out, however, that a stimulus is actually as complex (i.e., has many different qualities) as the ensuing reaction, which is in itself actually a chain of events triggered by the stimulus. For example, the visual perception of a moving stimulus can produce different images on the retina (in other words, the same optical stimulus can trigger different reactions). Hertz claimed that biologists are limited in accounting for these differences presumably because they neglect the phenomenological aspects of animal sensory perception. To this extent, Hertz put an emphasis on discovering laws explaining the relationship between external, objective conditions and events and inner constitution. This stood in stark contrast to more reductionistic or mechanical approaches in biology or comparative psychology at that time, which explained animal behavior, for example, in terms of trial-and-error learning or as being triggered and guided by automatic responses irrespective of peripheral factors in the environment that also play a role in determining behavior.

Although the potential impact of Hertz’s work was undoubtedly thwarted by an abrupt end to her experimental work, her research continued to influence—true to her conceptual orientation—work by biologists and psychologists. Some individuals were former students, such as Mercedes Gaffron, who completed her dissertation in 1934 on the stroboscopic vision of invertebrates and fish under Hertz’s supervision and immigrated to the United States in 1958 to take a position in the Psychology Department at Duke University where she worked with Karl Zener. Gaffron’s (1950a, b) work there focused on the phenomenological attributes and structure of spatial perception in regard to artwork. Another important scientist who was highly impressed by Hertz’s early experimental work on bees was Niko Tinbergen, who saw Hertz’s work and Frisch’s as providing models for his own doctoral dissertation on the homing behavior of the digger wasp.

In other cases they were scholars discovering Hertz’s work after her career had ended. The comparative physiologist Bernhard Hassenstein—Otto Koehler’s successor as chair at the University of Freiburg and Erich von Holst’s doctoral student—completed his dissertation on the physiological consequences of movement as a result of shifted images on the retina, based on Hertz’s work regarding the physiology of seen movement (Hertz, 1934, 1935b). Later Hassenstein’s research on this topic helped fuel the formation of a new field of research, biocybernetics. These examples show how multifaceted and enduring Hertz’s contributions to science were—their impact not yet even fully evaluated.

BIBLIOGRAPHY

WORKS BY HERTZ

“Wahrnehmungspsychologische Untersuchungen am Eichelhäher I” [Perceptual studies with jays I]. Zeitschrift für vergleichende Physiologie 7 (1928a): 144–194.

“Wahrnehmungspsychologische Untersuchungen am Eichelhäher II” [Perceptual studies with jays II]. Zeitschrift für vergleichende Physiologie 7 (1928b): 617–656.

“Die Organisation des optischen Feldes bei der Biene. III.” [The organization of the visual field in the bee. III]. Zeitschrift für vergleichende Physiologie 14 (1931): 629–674.

“Über figurale Intensitäten und Qualitäten in der optischen Wahrnehmung der Biene” [On figural intensities and qualities in the visual perception of bees]. Biologisches Zentralblatt 53 (1933): 10–40.

“Zur Physiologie der gesehenen Bewegung” [Concerning the physiology of seen movement]. Biologisches Zentralblatt 54 (1934): 250–264.

“Die Untersuchungen über den Formensinn der Honigbiene” [The experiments on the sense of shape in honeybees]. Die Naturwissenschaften 23 (1935a): 618–624.

“Zur Physiologie des Formen- und Bewegungssehens. II. Auflösungsvermögen des Bienenauges und optomotorische Reaktion” [Concerning the physiology of vision of shape and movement. II. Resolving power of the bee eye and the optomotor reaction]. Zeitschrift für vergleichende Physiologie 21 (1935b): 579–603.

“Le rapport de l’instinct et de l’intelligence dans le régne animal” [The relations between instinct and intelligence in the animal kingdom]. Journal de Psychologie Normale et Pathologique 34 (1937a): 324–341. (Originally translated into German “Die Beziehungen von Instinkt und Intelligenz im Tierreich” by Gisela Haus and later edited by S. Jaeger.)

With Augustus Daniel Imms. “On the Responses of the African Migratory Locust to Different Types of Background.” Proceedings of the Royal Society of London: Series B, Biological Sciences 122 (1937b): 281–297.

“New Experiments on Color Vision in Bees.” Journal of Experimental Biology 16 (1939): 1–8.

OTHER SOURCES

Duncker, Karl. On Problem-Solving. Psychological Monographs 58, no. 270. Washington, DC: American Psychological Association, 1945.

Frisch, Karl von. “Psychologie der Bienen” [Psychology of bees]. Zeitschrift für Tierpsychologie 1 (1937): 9–21.

Gaffron, Mercedes. Die Radierungen Rembrandts, Originale und Drucke. Studien über Inhalt und Komposition [The etchings of Rembrandt, originals and prints: Studies on content and composition]. Mainz, Germany: F. Kupferberg, 1950a.

———. “Right and Left in Pictures.” Art Quarterly 13 (1950b): 312–331.

Jaeger, Siegfried. “Vom erklärbaren, doch ungeklärten Abbruch einer Karriere—Die Tierpsychologin und Sinnesphysiologin Mathilde Hertz (1891–1975)” [On the accountable, though unaccounted for abrupt end of a career—The animal psychologist and sensory physiologist Mathilde Hertz (1891–1975)]. In Untersuchungen zur Geschichte der Psychologie und der Psychotechnik, edited by Horst Gundlach. Munich, Germany: Profil Verlag, 1996.

Kressley-Mba, Regina, and Siegfried Jaeger. “Rediscovering a Missing Link: The Sensory Physiologist and Comparative Psychologist Mathilde Hertz (1891–1975).” History ofPsychology 6 (2003): 379–396. Includes a complete bibliography of the scientist’s work.

Wertheimer, Max. “Untersuchungen zur Lehre von der Gestalt” [Studies on the theory of Gestalt]. Psychologische Forschung 4 (1923): 301–350.

Regina A. Kressley