Action at a distance: dependency sensitivity in a New World primate

Abstract

Sensitivity to dependencies (correspondences between distant items) in sensory stimuli plays a crucial role in human music and language. Here, we show that squirrel monkeys (Saimiri sciureus) can detect abstract, non-adjacent dependencies in auditory stimuli. Monkeys discriminated between tone sequences containing a dependency and those lacking it, and generalized to previously unheard pitch classes and novel dependency distances. This constitutes the first pattern learning study where artificial stimuli were designed with the species' communication system in mind. These results suggest that the ability to recognize dependencies represents a capability that had already evolved in humans’ last common ancestor with squirrel monkeys, and perhaps before.

Can squirrel monkeys learn an ABnA grammar? A re-evaluation of Ravignani et al. (2013)

“…Responding to grammatical and non-grammatical sequences in Tests 1 and 2 is displayed in Table 2. Results for Test 1 match the height of the bars in Figure 2 of Ravignani et al [2013]. Results for non-grammatical sequences in Test 2 are, however, are lower than in the original figure.…”

“…I acquired the data posted alongside the original article at http://rsbl.royalsocietypublishing.org/ content/9/6/20130852 and recast them as a table with the format displayed in Ravignani et al [2013] To ascertain that data acquisition did not introduce errors, this section reproduces the main analyses in Ravignani et al [2013]. It also serves to summarize the original results, in order to understand how they are affected by the factors discussed later.…”

“…The rationale for these choices, however, appears weak. I conclude with a Discussion that places the work of Ravignani et al [2013] in the broader perspective of working memory research and proto-linguistic abilities in animals.…”

“…According to Ravignani et al [2013], both Test 1 and 2 indicated that squirrel monkeys can detect the presence or absence of AB n A structure in novel sequences, including novel pitch patterns. Here, I show that this claim rests on several details of the authors' analysis, which are necessary to obtain conventionally "significant" results (p < 0.05) in both Test 1 and Test 2.…”

“…In addition, the statistical significance of results depends on specific choices of data analysis (dichotomization of the response variable and omission of certain data points) which appear to have a weak rationale. I also suggest that the task used by Ravignani et al [2013] may be fruitfully analyzed as an auditory sequence discrimination task that does not require specific proto-linguistic abilities. …”