Ronald J. Schusterman

A California Sea Lion (Zalophus Californianus) Is Capable of Forming Equivalence Relations

If a nonhuman animal matches the silhouette “crab” (A) to that of a “tulip” (B) and is further taught to match “tulip” (B) to the silhouette “radio” (C), will it immediately match “radio” (C) to “crab” (A)? To date formation of an equivalence relation of this type has not been demonstrated in animals. In our study, designed to give a sea lion match-to-sample experience with examples of sample and comparison stimuli switching roles, a 7-year-old female (Rio) was trained and tested with 30 potential classes, each consisting of 3 different shapes. Twelve of the 30 classes were used for training relational properties of symmetry and transitivity, and 18 classes were reserved for a final equivalence test. Following an initial failure to do symmetry on the first trial of novel relations (B→A: 8/12), Rio did symmetry (C→B: 11/12) and transitivity. (A→C: 11/12) before mastering equivalence on the first trial of 18 novel relations (C→A: 16/18). Results suggest that equivalence concepts are not mediated by language, but may be a prerequisite for linguistic competence.

California Sea Lions Are Capable of Semantic Comprehension

Two California sea lions (a 6-year-old female, Rocky, and a 3-year-old male, Bucky) were trained in a symbolic matching paradigm. Gestural signs produced by movements of the trainer’s arms and hands referred to types of objects, modifiers, and actions. Both sea lions were eventually trained with three-sign constructions consisting of Modifier + Object + Action in that order. An example of a three-sign sequence is Black Ball Mouth [glossed as “go over to the black ball (and not the gray or white balls or the black, white, and gray pipes) and place your open mouth on it]. Rocky’s modifiers consisted of size and color attributes, and Bucky’s modifiers consisted of different locations of the objects.After 24 months of training, Rocky had a comprehension vocabulary of 20 signs (5 modifiers, 10 objects, and 5 actions), and after 20 months of training, Bucky had a comprehension vocabulary of 16 signs (2 modifiers, 8 objects, and 6 actions). Semantic comprehension is considered to be demonstrated if an organism can follow directions when each sign is contrasted with every other in a series of commands. Currently, Rocky’s semantic comprehension consists of 190 three-sign combinations, and Bucky’s semantic comprehension consists of 64 three-sign combinations.

LOW-FREQUENCY AMPHIBIOUS HEARING IN PINNIPEDS : METHODS, MEASUREMENTS, NOISE, AND ECOLOGY

Aerial low-frequency (100-6400 Hz) hearing thresholds were obtained for one California sea lion (Zalophus californianus), one harbor seal (Phoca vitulina), and one northern elephant seal (Mirounga angustirostris). Underwater thresholds over a similar frequency range (75-6300 or 6400 Hz) were obtained for these three animals in addition to another California sea lion. Such data are critical, not only for understanding mechanisms about amphibious hearing and relating them to pinniped ecology and evolution, but also for identifying species at risk to man-made noise in the marine environment. Under water, the elephant seal was most sensitive, followed by the harbor seal and the sea lions. In air, the harbor seal was most sensitive, followed by the older of the two sea lions and the elephant seal. The following trends emerged from comparisons of each subjects aerial and underwater thresholds: (a) the sea lion (although possessing some aquatic modifications) is adapted to hear best in air; (b) the harbor seal hears almost equally well in air and under water; and (c) the elephant seals auditory system is adapted for underwater functioning at the expense of aerial hearing sensitivity. These differences became evident only when aerial and underwater thresholds were compared with respect to sound pressure rather than intensity. When such biologically relevant comparisons are made, differences in auditory sensitivity can be shown to relate directly to ecology and life history.

Underwater temporary threshold shift induced by octave-band noise in three species of pinniped.

Pure-tone sound detection thresholds were obtained in water for one harbor seal (Phoca vitulina), two California sea lions (Zalophus californianus), and one northern elephant seal (Mirounga angustirostris) before and immediately following exposure to octave-band noise. Additional thresholds were obtained following a 24-h recovery period. Test frequencies ranged from 100 Hz to 2000 Hz and octave-band exposure levels were approximately 60-75 dB SL (sensation level at center frequency). Each subject was trained to dive into a noise field and remain stationed underwater during a noise-exposure period that lasted a total of 20-22 min. Following exposure, three of the subjects showed threshold shifts averaging 4.8 dB (Phoca), 4.9 dB (Zalophus), and 4.6 dB (Mirounga). Recovery to baseline threshold levels was observed in test sessions conducted within 24 h of noise exposure. Control sessions in which the subjects completed a simulated noise exposure produced shifts that were significantly smaller than those observed following noise exposure. These results indicate that noise of moderate intensity and duration is sufficient to induce TTS under water in these pinniped species.

Artificial Language Comprehension in Dolphins and Sea Lions: The Essential Cognitive Skills

First, we review recent efforts to demonstrate language competence in apes and dolphins. Then, with techniques originally devised by Herman in his artificial language studies with dolphins (Tursiops truncatus), we show that smaller brained sea lions (Zalophus californianus), like larger brained dolphins, are capable of comprehending signals about a relationship between two designated objects. The language we used consisted of signs designating properties of size, brightness, or location (modifiers), types of objects, and actions. The results of our experiments with two sea lions support Premack’s notion that Herman’s dolphins (as well as our sea lions) relied principally on two phrase structure rules to comprehend thousands of novel, unique messages that could be transmitted gesturally by a “blind” human signaler. One rule instructs the animal to perform an action directly on an object designated by an object signal and one or two optional modifiers. The instruction takes the form (Modifier) + Object + Action. The second rule instructs the animal to perform an action relative to two designated objects. The object to be transported and the goal object were assigned their particular roles by their position in the sign sequence. The relational instruction takes the form (Modifier) + Object A + (Modifier) + Object B + Action. Reversing the order of the two object signals in the string reversed the meaning of the message. For both sea mammals we found support for Herman’s notion that the critical constraint on the application of the second rule is memory for Object A (the goal item). The variables influencing memory for the goal item were: (a) the number of objects available, (b) bias for certain goal items, (c) whether the goal item was fixed in space, that is whether it was a transportable or nontransportable object, and (d) whether the goal item (Object A) and the transported item were reversed on successive trials.We conclude that both dolphins and sea lions can be taught to comprehend sentence-like instructions. The simplified language learned by these marine mammals depends on the following learned cognitive skills: (a) acquiring a repertoire of arbitrary conditional relations between signals and objects, (b) perceiving and conceptualizing objects and events within class and relational categories, and (c) acquiring a conditional sequential discrimination.

Artificial language comprehension and size transposition by a California sea lion (Zalophus californianus)

A variation of the conditional discrimination procedure defines relations between stimuli (for example, gestural signs and their referents), and it has been used to study language comprehension in California sea lions. The animals followed instructions given by a trainers gestures designating properties of size, brightness, and location (adjectives), types of objects (nouns), and actions (verbs). The signs can be combined and recombined according to a conditional sequence or syntax. In this study, we sought to determine whether adjectives for size had an absolute meaning, that is, small and large, as well as a comparative meaning, that is, smaller and larger. A sea lion, Rocky, was given experience with signs designating standard small and large spheres in commands like LARGE BALL MOUTH. On transposition tests, the small ball was removed and the previously designated large ball was paired with an even larger one. The results showed that the adjectives had both an absolute and a relative meaning. Object choices and searching behavior revealed that the sea lion processed information about the relation of size as well as about the specific characteristics of the sizes of spheres that instantiated the relations.

Why pinnipeds don’t echolocate

Odontocete cetaceans have evolved a highly advanced system of active biosonar. It has been hypothesized that other groups of marine animals, such as the pinnipeds, possess analogous sound production, reception, and processing mechanisms that allow for underwater orientation using active echolocation. Despite sporadic investigation over the past 30 years, the accumulated evidence in favor of the pinniped echolocation hypothesis is unconvincing. We argue that an advanced echolocation system is unlikely to have evolved in pinnipeds primarily because of constraints imposed by the obligate amphibious functioning of the pinniped auditory system. As a result of these constraints, pinnipeds have not developed highly acute, aquatic, high frequency sound production or reception systems required for underwater echolocation. Instead, it appears that pinnipeds have evolved enhanced visual, tactile, and passive listening skills. The evolutionary refinement of alternative sensory systems allows pinnipeds to effectively forage, navigate, and avoid predators under water despite the lack of active biosonar capabilities.

Masking in three pinnipeds: Underwater, low-frequency critical ratios

Behavioral techniques were used to determine underwater masked hearing thresholds for a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Octave-band white noise maskers were centered at five test frequencies ranging from 200 to 2500 Hz; a slightly wider noise band was used for testing at 100 Hz. Critical ratios were calculated at one masking noise level for each test frequency. Above 200 Hz, critical ratios increased with frequency. This pattern is similar to that observed in most animals tested, and indicates that these pinnipeds lack specializations for detecting low-frequency tonal sounds in noise. However, the individual pinnipeds in this study, particularly the northern elephant seal, detected signals at relatively low signal-to-noise ratios. These results provide a means of estimating zones of auditory masking for pinnipeds exposed to anthropogenic noise sources.

Transfer of visual identity matching-to-sample in two california sea lions (zalophus californianus)

In order to assess the abilities of two California sea lions to generalize an identity concept, both animals were taught a two-choice, visual matching-to-sample task. We hypothesized that initial identity-matching problems would be learned as conditional (if...then) discriminations but that an identity concept would emerge after training numerous exemplars of identity matching. After training with 15 two-stimulus identity matching-to-sample problems, transfer tests consisting of 15 novel problems were given to the animals. Pass-fail criteria were defined in terms of performance on Trial 1 of each test problem, performance on test trials compared with baseline trials, and performance on four-trial problem blocks. One sea lion passed on the second transfer test and the other passed on the third; both demonstrated successful generalization of an identity concept by all criteria used. A second experiment consisted of presentation of stimuli previously learned in a different context (arbitrary matching-to-sample). Both subjects immediately applied an identity concept to accurately solve these new problems. These tests conclusively demonstrate transfer of an identity matching rule in California sea lions.

Underwater temporary threshold shift in pinnipeds : Effects of noise level and duration

Behavioral psychophysical techniques were used to evaluate the residual effects of underwater noise on the hearing sensitivity of three pinnipeds: a California sea lion (Zalophus californianus), a harbor seal (Phoca vitulina), and a northern elephant seal (Mirounga angustirostris). Temporary threshold shift (TTS), defined as the difference between auditory thresholds obtained before and after noise exposure, was assessed. The subjects were exposed to octave-band noise centered at 2500 Hz at two sound pressure levels: 80 and 95 dB SL (re: auditory threshold at 2500 Hz). Noise exposure durations were 22, 25, and 50 min. Threshold shifts were assessed at 2500 and 3530 Hz. Mean threshold shifts ranged from 2.9-12.2 dB. Full recovery of auditory sensitivity occurred within 24 h of noise exposure. Control sequences, comprising sham noise exposures, did not result in significant mean threshold shifts for any subject. Threshold shift magnitudes increased with increasing noise sound exposure level (SEL) for two of the three subjects. The results underscore the importance of including sound exposure metrics (incorporating sound pressure level and exposure duration) in order to fully assess the effects of noise on marine mammal hearing.