Effects of brief time delays on matching-to-sample abilities in capuchin monkeys (Sapajus spp.)

Abstract

Traditionally, studies of delayed matching-to-sample (DMTS) tasks in nonhuman species have focused on the assessment of the limits of the retrieval of information stored in short-and longterm memory systems. However, it is still unclear if visual recognition in these tasks is affected by very brief delay intervals, which are typically used to study rapidly decaying types of visual memory. This study aimed at evaluating if tufted capuchin monkeys' ability to recognise visual stimuli in a DMTS task is affected by (i) the disappearance of the sample stimulus and (ii) the introduction of delay intervals (0.5, 1.0, 2.0 and 3.0 seconds) between the disappearance of the sample and the presentation of the comparison stimuli. The results demonstrated that the simple disappearance of the sample and the introduction of a delay of 0.5 seconds did not affect capuchins' performance either in terms of accuracy or response time. A delay interval of 1.0 second produced a significant increase in response time but still did not affect recognition accuracy. By contrast, delays of 2.0 and 3.0 seconds determined a significant increase in response time and a reduction in recognition accuracy. These findings indicate the existence in capuchin monkeys of processes enabling a very accurate retention of stimulus features within time frames comparable to those reported for humans' sensory memory (0.5-1.0 seconds). The extent to which such processes can be considered analogous to the sensory memory processes observed in human visual cognition is discussed. We examine capuchin monkeys' ability to match visual stimuli after brief delays. 0.5 sec intervals do not affect either response accuracy or response time.  1.0 sec intervals do not affect response accuracy but increase response time. 2.0 and 3.0 sec intervals decrease response accuracy and increase response time. Effects consistent with those ascribed to iconic memory in humans. Research Highlights Responses to the ReviewerWe were extremely pleased that the reviewer was satisfied with the vast majority of our revisions and that s/he felt that we had been very responsive and addressed most of her/his concerns. We are also pleased to read that the reviewer felt that all her/his specific comments have been addressed.We have now further revised the article in several places (P 4 lines 46-48; P 6 lines 53-59; P 7 lines 1-3; P 13 lines 44-49; P 14 lines 1-7; P 18 lines 48-54; P 18 line 56 -P 19 line 1) in order to make it absolutely clear that we make no claims regarding the high-capacity of the memory system that we have observed in capuchin monkeys so that, in that respect it could be considered analogous to human iconic memory. All our claims are based on analyses of the effects of time delay which, because they suggest a discontinuous function of the delays, can be considered indicative of separate memory processes at early stages of the encoding of visual information in monkeys.As suggested by the reviewer we now present effect sizes for paired t tests and 95% confidence in...

Short-term memory effects on visual global/local processing in tufted capuchin monkeys (Sapajus spp.).

“…Such a significant increase of the response time for delay intervals equal or longer than 572 1.0 sec has also been documented in capuchins (Truppa et al, 2014) …”

“…This suggests that the local advantage observed in simultaneous and 473 zero-delay conditions in capuchin monkeys cannot be explained by a selective 474 engagement of the dorsal visual system induced by fast responding to stimuli that are 475 perceptually available when acting upon them. Of particular relevance for this study are 476 previous data by Truppa et al (2014) showing that, when matching conditions identical 477 to those of the present study were presented using non-hierarchical stimuli, capuchins 478 were able to solve the task with up to 3 sec delay. Therefore, it seems that the encoding 479 However, the results of this study show that global information is either encoded less 483 accurately or deteriorates more rapidly in memory than local information.…”

Self-control depletion in tufted capuchin monkeys (Sapajus spp.): does delay of gratification rely on a limited resource?

“…All subjects had been previously tested in the self-control task used in the present study ( Addessi et al, 2013 ) and were already familiar with the computerized apparatus used in the Cognitive Depletion Experiment (see below) because they took part in previous studies involving computerized Matching-to-Sample and two-alternative choice tasks (e.g., Truppa et al, 2010 , 2011 , 2014 , 2015 ).…”

Does Presentation Format Influence Visual Size Discrimination in Tufted Capuchin Monkeys (Sapajus spp.)?

“…The other monkeys were familiarised to with the apparatus immediately before starting this experiment. In the Image condition, all the subjects were already familiar with the computerised workstation because they took part in a training programme with computerised matching-to-sample tasks [ 14 – 16 ]. None of the subjects had been tested with a computerised two-alternative choice task before.…”

“…The necessity to carry out in-depth analyses of cognitive processes has led to the development of increasingly sophisticated methods for data collection. The last few decades in particular have seen widespread use of computerised procedures in an increasing number of taxonomic groups, such as apes [ 6 – 9 ], Old World monkeys [ 10 – 13 ], New World monkeys [ 14 – 22 ], dogs [ 23 , 24 ], horses [ 25 ], pigeons [ 26 – 33 ], corvids [ 34 ], and tortoises [ 35 ]. Despite this trend, little is known about the generalisability of such computerised methods to more natural settings involving ‘real’ three-dimensional stimuli (e.g., food).…”