Journal of Comparative Psychology

What is it like to hear quantities? Testing dolphins on classic number estimation using a sonar setup.
The featured article by Sakurai and Tomonaga (2024) in this issue has set out to test to what extent dolphins can estimate relative differences between pairs of object numbers by echolocation. For this they used three consecutive experiments with multiple controls and compared their data statistically to existing data from visual experiments done on other species. Previous studies already indicate that dolphins can visually estimate relative numerosity (e.g., Jaakkola et al., 2005; Yaman et al., 2012). Therefore, the goal of the present study was to investigate the dolphin’s capacity to apply Weber’s law (quantity judgments are more accurate proportional to the quantities investigated) to two sets of object quantities under sonar evaluation. (PsycInfo Database Record (c) 2024 APA, all rights reserved)
Hearing “number”? Relative quantity judgments through the echolocation by bottlenose dolphins (Tursiops truncatus).
Dolphins are known to recognize their environment through echolocation. Previous studies have reported that they can discriminate the shape, size, thickness, and even material of objects through echolocation. However, little is known about the discrimination of quantities other than size and thickness (e.g., the number of objects). It is also unclear whether Weber’s law (i.e., ratio dependency) holds for quantity discrimination through echolocation. In this study, we examined relative quantity judgments of visually occluded objects presented underwater by bottlenose dolphins. We found that they could discriminate pairs of same-sized objects ranging from one to eight, with performance improving as the difference ratio between the two numbers increased. In addition, their performance also improved as the magnitude of the number of objects involved increased. An additional test revealed that the accuracy of discrimination through echolocation was comparable to that of visual relative quantity judgments of the objects presented above water. On the other hand, under the condition that the overall size of each object (i.e., the sum of areas) was incongruent with the number of objects, performance was lower than when number and size were covarying. However, even within the incongruent condition, the effect of the number ratio was still observed, suggesting that the dolphins might have used various types of quantity information, such as number and size, flexibly to solve the task. (PsycInfo Database Record (c) 2024 APA, all rights reserved)
Serial pattern learning: Pigeons (Columba livia) prefer an improving schedule over an initially easier fixed ratio schedule.
Serial pattern learning describes behavior in which a subject anticipates not only the time and effort needed for the next reinforcer but also the pattern of time and effort to reinforcers after the first. Chandel et al. (2021) found that pigeons left a progressive (increasing ratio) schedule earlier than would have been optimal. They argued that the pigeons anticipated the harder-to-obtain reinforcers beyond the next one. In the present experiments, pigeons were trained on a progressive schedule for which each reinforcer was successively easier to obtain. However, the initial choice was between a fixed ratio schedule (FR23) for which a reinforcer was easier to obtain than the first reinforcer on the improving progressive schedule (32 pecks). Delayed discounting theory suggests that the pigeons would prefer the FR23 because more immediate reinforcers should be preferred, whereas serial pattern learning suggests that the progressive schedule might be preferred because easier-to-obtain reinforcers would follow the initially harder 32 pecks. In Experiment 1, a preference for the fixed ratio schedule was not found, however, in Experiment 2, when the two alternatives were equated for the number of reinforcers that could be obtained on each trial, a significant preference for the improving progressive schedule was found. The results of Experiment 2 were consistent with the serial pattern learning hypothesis. The pigeons did not choose the more immediate reinforcer associated with fixed ratio alternative. Rather, they showed a preference for the improving progressive schedule for which later reinforcers would be easier to obtain. (PsycInfo Database Record (c) 2024 APA, all rights reserved)
Using isochrony, but not meter, to discriminate rhythmic sequences in rats (Rattus norvegicus).
Meter induction is a key process for rhythm perception. However, while some nonhuman animals readily detect temporal regularities and perceive beats in auditory sequences, there is no consistent evidence that they extract metrical structures. In the present experiment, we familiarized rats (Rattus norvegicus) to auditory rhythmic sequences that evoked a duple or a triple meter. We then tested their recognition of these familiar sequences when pitted against novel sequences that evoked no meter (isotonic), evoked a different meter (either duple or triple), or were nonmetrical (nonisochronous). The animals only discriminated isochronous from nonisochronous sequences. However, we found no evidence for meter induction, as the animals did not discriminate familiar from isotonic sequences or from sequences with a different meter. The findings suggest that, under a familiarization paradigm, the natural tendency of the animals is to focus on temporal rather than melodic changes to recognize rhythmic sequences. (PsycInfo Database Record (c) 2024 APA, all rights reserved)
Cross-modal perception of puppies and adult conspecifics in dogs (Canis familiaris).
Understanding conspecifics’ age classes is crucial for animals, facilitating adaptive behavioral responses to their social environment. This may include gathering and integrating information through multiple modalities. Using a cross-modal preferential-looking paradigm, we investigated whether dogs possess a cross-modal mental representation of conspecific age classes. In Experiment 1, dogs were presented with images of an adult dog and a puppy projected side by side on a wall while a vocalization of either an adult dog or a puppy was played back simultaneously. To test the effect of relative body size between adult dog and puppy images, two size conditions (natural size and same size) were employed for visual stimuli. We examined dogs’ looking behavior in response to cross-modally matched versus mismatched stimuli. We predicted that if dogs have cross-modal representations of age classes, they would exhibit prolonged attention toward matched images compared to mismatched ones. In Experiment 2, we administered the same paradigm within an eye-tracking experiment to further improve the measurement quality of dogs’ looking times. However, dogs’ looking times in either experiment did not demonstrate significant differences based on the match or mismatch between image and vocalization. Instead, we observed a size effect, indicating dogs’ increased attention toward larger adult dog images compared to smaller puppy images. Consequently, we found no evidence of cross-modal representation of age class in dogs. Nonetheless, we found increased looking time and pupil size upon hearing puppy vocalizations compared to adult vocalizations in Experiment 2, suggesting that dogs exhibited heightened arousal when hearing puppy whining. (PsycInfo Database Record (c) 2024 APA, all rights reserved)
No evidence of attentional bias toward threatening conspecific and allospecific faces in capuchin monkeys (Sapajus [Cebus] apella) using a dot-probe task.
The ability to quickly perceive and interpret threatening facial expressions from others is critical for successfully maintaining group cohesion in social nonhuman primate species. Rapid detection of threatening or negative stimuli in the environment compared to neutral stimuli, referred to as an attentional bias toward threat, is adaptive in that faster threat detection can lead to greater survival outcomes. However, the evolutionary roots of attentional bias formation toward social threat are not well understood. The present study investigated attentional biases toward social threat and the factors associated with them, including underlying hormonal mechanisms, in socially housed capuchin monkeys. Attentional biases were assessed using a dot-probe task that measured capuchins’ latency to respond to a target using a joystick after viewing threatening or neutral conspecific or allospecific faces or nonface stimuli. In our first study, we examined how age, dominance status, sex, and cortisol level related to attentional biases. In our second study, we examined how manipulated oxytocin (OT) influenced attentional biases. Capuchin monkeys did not show attentional biases toward threatening faces or objects, but they showed attentional avoidance of scrambled familiar conspecific face stimuli. Cortisol and social rank were associated with attentional bias toward threat in the capuchin monkeys that participated in this study, which suggests that stress and dominance relate to attentional bias toward social threat. Manipulated OT increased attentional avoidance of scrambled familiar and unfamiliar face images, but not unscrambled faces or objects. Overall, we did not find compelling evidence of attentional biases toward social threat in capuchin monkeys. (PsycInfo Database Record (c) 2024 APA, all rights reserved)
Differences in paradoxical choice between pigeons (Columba livia) and rats (Rattus norvegicus): The problem of cue trackability.
Organisms are believed to attempt to maximize their net energy intake while foraging. The paradoxical choice task shows that they may instead prefer to obtain information rather than primary reward when the outcome is uncertain. That is, they prefer stimuli that consistently predict food or no food (informative option), to stimuli that inconsistently predict both food and no food in larger amounts (noninformative option). This task also seems to indicate that some species (like pigeons, Columba livia, and starlings, Sturnus vulgaris) are more prone to choose the informative option, while other species (like rats, Rattus norvegicus, and humans, Homo sapiens) tend to favor reward procurement through the noninformative option. There is empirical evidence for and against this view. However, an analysis of the literature suggests that species differences in paradoxical choice might be less pronounced than often believed. We argue that pigeons and rats are usually not tested under conditions that are motivationally equivalent for both species—in particular, the opportunities to track consistent stimulus–food pairings are less often met in the rat studies than in the pigeon studies. (PsycInfo Database Record (c) 2024 APA, all rights reserved)

Journal of Comparative Psychology - Vol 138, Iss 4