Kellogg's Initial Research Involving Echolocation In Humans
Sparked by his success in discovering that porpoises use echo ranging to distinguish objects in their local environment, Kellogg turned his research to the possibility that blind humans might do the same. He outlined this idea and the research projects he envisioned in the introduction to his 1962 article "Sonar System of the Blind" which appeared in Science (1962, 137, pp 399 - 404):
"Since it had been shown that porpoises can distinguish between objects of different sizes by echo ranging , the question arose as to whether the blind could accomplish the same thing. If the answer was "Yes," would it then be possible to obtain quantitative or numerical measurements of this ability? Could threshold fractions for echo ranging be calculated in the same way that DI/I is computed for visual distance and for size perception? What would the psychophysical function look like? Would Weber's law hold in such a case? Last but not least, do we have here a procedure for comparing quantitatively the sonar of human beings with that of the bat and the porpoise?"
Kellogg found it surprising that human beings might not use sonic echoes considering that the vast amount of other animals which employ sonar systems do not possess the superior neural and sensory equipment found in humans.
Kellogg carried out a series of experiments aimed at comparing the sensitivity of blind and sighted humans to detect changes in the distance, size, and texture of various objects. Four male college students acted as the participants (two blind and two sighted). One participant had been blind for ten years and the other for five. The sighted students were blindfolded for the tests and served as controls. Students were tested individually while seated in a room where a series of flat discs of different sizes and materials, hung by a system of ropes and pulleys, were suspended at head level. The discs could be remotely moved closer to or away from the participant's face. The task was to report if the disc was nearer or farther, larger or smaller, and made from the same material as the previously presented disc. The participants where allowed to make any noises they wished in order to try to determine the answer to the above questions.
The arrangement for presenting the stimuli in the distance-discrimination or depth-perception experiment. The disc used as a target is silently moved to one of seven fixed positions.( Note: This is room 318 in the Psychology (Eppes) Building at FSU)
Both of the blind participants made talking, hissing, singing, whistling, finger-snapping, and tongue-clicking sounds while trying to carry out the task. However, the preferred sound was the human voice. The blind participants used single word repetition, speech patterns, and one even sang the diatonic scale. The sighted participants used vocal signals for the most part. Both of the blind participants oscillated their head from side to side while emitting their chosen sound in a way very similar to the bottlenose dolphin. The sighted participants did not employ head oscillations nearly as much.
In distance perception, the sighted participants generally performed close to chance level. The blind participants performed better. One student was able to detect a 4-inch change in the position of a 1-foot diameter disc placed two feet away from him.
Size discrimination was more difficult. The accuracy of size-detection by one blind participant was fairly good at a distance of 12 inches, particularly when larger discs were used; accuracy declined at greater distances. The other blind participant was less accurate at 12-inch distance, and did not show differing degrees of accuracy at different distances. Kellogg believed that the difference in performance by the blind participants was due more to the apparatus than to the participants' abilities.
The following Table shows that the two blind participants did amazingly well in recognizing changes in different materials. A score of 59% or higher indicated a judgment that differed significantly from chance at the 0.01 level of confidence. In general, the results point to a distinction between "hard" and "soft" (or poor) reflecting surfaces. For example, echoes from wood and glass were indistinguishable, as were echoes from glass and metal. Surprisingly, denim cloth and velvet were differentiated 86.5% of the time.
were discriminated by two blind subjects (from Table 4; Kellogg, 1962)
In all of the experiments, the judgments of the four participants were made by listening to echoes reflected back from separate targets. The object of the study was not to compare the effectiveness of the different signals the blind used, but to determine what signals the blind would use and if those signals were at all effective. Kellogg was impressed by the obtained results and felt he had demonstrated that some blind humans can make surprisingly accurate assessment of the properties of objects in their environments. Future research, he thought, might produce results that compare favorably with the abilities of the porpoise and the bat.