A longitudinal assessment of vocabulary retention in symbol-competent chimpanzees (Pan troglodytes)

Sign Language Studies with Chimpanzees in Sanctuary

Adult chimpanzees Tatu and Loulis lived at the Fauna Foundation sanctuary. They had acquired signs of American Sign Language (ASL) while young and continued to use them as adults. Caregivers with proficiency in ASL maintained daily sign language records during interactions and passive observation. Sign checklists were records of daily vocabulary use. Sign logs were records of signed interactions with caregivers and other chimpanzees. This study reports sign use from eight years of these records. Tatu and Loulis used a majority of their base vocabularies consistently over the study period. They used signs that they had acquired decades earlier and new signs. Their utterances served a variety of communicative functions, including responses, conversational devices, requests, and descriptions. They signed to caregivers, other chimpanzees, including those who did not use signs, and to themselves privately. This indicates the importance of a stimulating and interactive environment to understand the scope of ape communication and, in particular, their use of sign language.

A Preliminary Assessment of Compassion Fatigue in Chimpanzee Caregivers

Compassion fatigue is defined as "traumatization of helpers through their efforts at helping others". It has negative effects on clinicians including reduced satisfaction with work, fatigue, irritability, dread of going to work, and lack of joy in life. It is correlated with patients' decreased satisfaction with care. Compassion fatigue occurs in a variety of helping professions including educators, social workers, mental health clinicians, and it also appears in nonhuman animal care workers. This study surveyed caregivers of chimpanzees using the ProQOL-V to assess the prevalence of compassion fatigue among this group. Compassion satisfaction is higher than many other types of animal care workers. Conversely, this group shows moderate levels of burnout and secondary traumatic stress; higher levels than other types of animal care workers and many medical professions. While compassion fatigue has an effect on the caregiver's experience, it has potential to affect animal welfare. Caregivers are an integral part of the chimpanzee social network. Compassion fatigue affects the caregiver's attitude, this could in turn affect the relationship and degrade the experience of care for captive chimpanzees. Compassion fatigue can be mitigated with professional development, mindfulness training, interrelationships among staff, and specialized training. This preliminary assessment indicates the work ahead is educating caregivers about compassion fatigue and implementing procedures in sanctuaries to mitigate burnout and secondary traumatic stress.

A chimpanzee recognizes varied acoustical versions of sine-wave and noise-vocoded speech

Previous research demonstrated that a language-trained chimpanzee recognized familiar English words in sine-wave and noise-vocoded forms (Heimbauer et al. Curr Biol 21:1210-1214, 2011). However, those results did not provide information regarding processing strategies of the specific acoustic cues to which the chimpanzee may have attended. The current experiments tested this chimpanzee and adult humans using sine-wave and noise-vocoded speech manipulated using specific sine-waves and a different number of noise bands, respectively. Similar to humans tested with the same stimuli, the chimpanzee was more successful identifying sine-wave speech when both SW1 and SW2 were present - the components that are modeled on formants F1 and F2 in the natural speech signal. Results with noise-vocoded speech revealed that the chimpanzee and humans performed best with stimuli that included four or five noise bands, as compared to those with three and two. Overall, amplitude and frequency modulation over time were important for identification of sine-wave and noise-vocoded speech, with further evidence that a nonhuman primate is capable of using top-down processes for speech perception when the signal is altered and incomplete.

Post-event misinformation effects in a language-trained chimpanzee (Pan troglodytes)

Errors of source monitoring are widespread human memory challenges, and our memories are subject to distortion upon the presentation of subsequent misinformation. Less is known about if and when misinformation effects occur in nonhuman species' memory. Here we tested a symbol-trained chimpanzee's recall memory of a hidden food item's identity after a 10-min delay. During this delay, the subject was sometimes (depending on the condition) shown consistent or inconsistent video information about the identity of the food, before being asked to name the item to a second experimenter blind to the reward and condition. Across all conditions, our subject, Sherman, correctly named the food item at above chance levels. In the Inconsistent condition, in which Sherman was shown a video with misleading information, his performance was the worst of all conditions (although accuracy was still high). Interestingly, however, during three of the four trials in this condition in which Sherman made a mistake, he incorrectly named the food item shown during the misleading video information. These results provide evidence that chimpanzees, like humans, may be vulnerable to misinformation effects, even when that misleading information is presented in a different modality (video) than the original live event memory, demonstrating further commonality between human and ape memory systems.

Long-Term Memory of Past Events in Great Apes

It has been claimed that the ability to recall personal past events is uniquely human. We review recent evidence that great apes can remember specific events for long periods of time, spanning months and even years, and that such memories can be enhanced by distinctiveness (irrespective of reinforcement) and follow a forgetting curve similar to that in humans. Moreover, recall is enhanced when apes are presented with features that are diagnostic of the event, consistent with notions of encoding specificity and cue overload in human memory. These findings are also consistent with the involuntary retrieval of past events in humans, a mode of remembering that is thought to be less cognitively demanding than voluntary retrieval. Taken together, these findings reveal further similarities between the way humans and animals remember past events and open new avenues of research on long-term memory in nonhuman animals.

Animal Memory: Chimpanzees Anticipate What Comes Next in Short Movies

A recent study shows that chimpanzees remember a movie they viewed one day earlier, and their eye movements show that they anticipate certain actions in that movie before those actions occur by looking to parts of the scene that are about to become relevant to the storyline.

Go when you know: Chimpanzees' confidence movements reflect their responses in a computerized memory task

Three chimpanzees performed a computerized memory task in which auditory feedback about the accuracy of each response was delayed. The delivery of food rewards for correct responses also was delayed and occurred in a separate location from the response. Crucially, if the chimpanzees did not move to the reward-delivery site before food was dispensed, the reward was lost and could not be recovered. Chimpanzees were significantly more likely to move to the dispenser on trials they had completed correctly than on those they had completed incorrectly, and these movements occurred before any external feedback about the outcome of their responses. Thus, chimpanzees moved (or not) on the basis of their confidence in their responses, and these confidence movements aligned closely with objective task performance. These untrained, spontaneous confidence judgments demonstrated that chimpanzees monitored their own states of knowing and not knowing and adjusted their behavior accordingly.