Rhesus Monkeys (Macaca mulatta) Maintain Learning Set Despite Second-Order Stimulus-Response Spatial Discontiguity

Abstract

In many discrimination-learning tests, spatial separation between stimuli and response loci disrupts performance in rhesus macaques. However, monkeys are unaffected by such stimulusresponse spatial discontiguity when responses occur through joystick-based computerized movement of a cursor. To examine this discrepancy, five monkeys were tested on a learning-set task that required them to touch computer-graphic "levers" (which differed in location across experimental phases) with a cursor in order to select an associated test stimulus. The task produced both first-order Uoystick and lever) and second-order (lever and stimuli) spatial discontiguity between the stimuli to be discriminated and the discriminative response. Performance was significantly better than chance for all lever locations including locations in which selection of the correct lever required moving the cursor away from the positive stimulus. Thus, rhesus macaques do not attend simply to the region around the cursor in these computerized tests, but rather they attend to relevant stimulus loci eVl en when these are discontiguous with response and reward areas.

Old World monkeys are more similar to humans than New World monkeys when playing a coordination game

“…For example, spatial discontiguity between response loci and stimuli was recognized as an obstacle to learning in animals [7][8][9]. However, training primates to use a joystick gets past that problem of discontiguity and produces markedly different patterns of results [10,11], and the same may be true for performance in economic games. Thus, comparing our previous results to those from a computer task may help to highlight factors that affect decision-making.…”

The importance of risk tolerance and knowledge when considering the evolution of inequity responses across the primates

“…In particular, work with ten primate species spread across the great apes, Old World monkeys, and New World monkeys demonstrates that inequity is most common in species that show high levels of cooperation with non-kin, non-pair social group members (Brosnan 2011). That is, primates that routinely form coalitions and alliances for support, rank acquisition or territory defense, cooperatively hunt, or otherwise socially cooperate, including chimpanzees (Brosnan, Schiff et al 2005;Brosnan, Talbot et al 2010), capuchin monkeys (Brosnan and de Waal 2003;van Wolkenten, Brosnan et al 2007;Fletcher 2008;Takimoto, Kuroshima et al 2009), macaques (McCleam andHarlow 1954;Beran, Rumbaugh et al 2007), and, possibly, bonobos (Bräuer, Call et al 2009), respond to inequity while other, often closely related (Talbot, Freeman et al 2011) and equally largebrained species (Meyer, Polidora et al 1961;Bräuer, Call et al 2009) do not. Moreover, these results do not map on to other distributions, such as those based on brain size, performance on cognitive tasks, or extent of sociality (Brosnan 2011).…”