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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Behavioural Processes 85 (2010) 246–251 Contents lists available at ScienceDirect Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc Functional relationships for determining similarities and differences in comparative cognition Anthony A. Wright ∗ Department of Neurobiology and Anatomy, Medical School, University of Texas Health Center at Houston, P.O. Box 20708, Houston, TX 77225, United States article info abstract Article history: Pigeons, capuchin monkeys and rhesus monkeys were trained in nearly identical same/different tasks Received 6 May 2010 with an expanding 8-item training set and showed qualitatively similar functional relationships: increas- Received in revised form 22 July 2010 ing novel-stimulus transfer (i.e., concept learning) as a function of the training-set size and the level of Accepted 30 July 2010 transfer eventually becoming equivalent to baseline training performance. There were also some quan- titative functional differences: pigeon transfer increases were more gradual and baseline-equivalent Keywords: transfer occurred at a larger set size (256 items) than for monkeys (128 items). Other pigeon groups Abstract concepts trained at 32 and 64-item initial set sizes showed improved transfer (relative to expanding the 8-item Same–different Cognitive modules training set), equivalent to the monkey species’ transfer at these same training set sizes. This finding Evolution of equivalent concept learning over a portion of the functional range (8, 32, and 64 items or 64–4096 Monkeys training pairs) is discussed in terms of species differences: carryover effects from smaller-set training, Pigeons evolved neural systems, cognitive and cortical modules, and general distributed learning systems for “higher-order” cognitive abilities. © 2010 Elsevier B.V. All rights reserved. Recent articles have rekindled the debate about which human The approach taken in this article is that functional relation- cognitive abilities (e.g., tool use, teaching, social competence, ships can better identify similarities and differences in cognitive theory of mind, abstract-concept learning, analogical reasoning, ability. Functional relationships are measures of cognitive behavior domain-general cognition) are unique and distinguish humans at several points along a continuum of a critical variable. Functional from other animals (Herrmann et al., 2007; Penn et al., 2008; relationships can identify aspects that are similar and aspects that Premack, 2007, 2010). are different. Tests at only a single value (on the continuum) are Proposals of special cognitive abilities are not limited to humans. more likely to discover differences with little hope of discovering Comparative cognition has a long history of focusing on which qualitative similarity between functional relationships because lots species can or cannot learn certain cognitive tasks. Hierarchies of of variables can affect the absolute performance level. cognitive ability have been constructed on the basis of such learning Similarities and differences in cognitive abilities may be divided differences often with abstract-concept learning or analogical rea- into two general categories: qualitative similarity and quantita- soning at the top (e.g., D’Amato et al., 1985; Herman et al., 1989; tive similarity. From the standpoint of how some cognitive ability Herrnstein, 1990; Premack, 1978, 1983a,b; Thomas, 1980, 1996; works, qualitative similarity is perhaps the more important. Nev- Thompson, 1995; Thompson and Oden, 2000). For the most part, ertheless, I will argue that functional relationships are necessary to the concentration is on which species has what cognitive ability show either. Take the example of visual list memory across species and which species does not (cf., Tomasello and Call, 1997). Many as diverse as pigeons, new and old world monkeys, and humans. tests are all-or-none; the species learns or not, transfers or not, All of these species showed similar changes in their serial position etc. Learning and (transfer) performance can fail in many more functions (SPFs) as the retention delay is increased (e.g., see Wright, ways than it can succeed; such failures, including partial failures, 1998, 2007; Wright et al., 1985). The SPFs showed strong recency are difficult to interpret (e.g., Macphail, 1985, 1996). May be the effects (last item memory) at short retention delays. The primacy right experiment just was not conducted for the task to be learned effect (good first item memory) came in at intermediate delays and or transfer performance to be equivalent to the baseline training strengthens as delay is extended. The recency effect waned as the performance. primacy effect strengthened. These similar SPFs showed qualitative similarity in visual list-memory processing across these species. Notwithstanding the qualitative similarity, there were some quan- ∗ Corresponding author. Tel.: +1 713 500 5627. titative differences. For example, the time scale of these changes E-mail address: [email protected]. varied across species with these changes taking place most rapidly 0376-6357/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.beproc.2010.07.018 Author's personal copy A.A. Wright / Behavioural Processes 85 (2010) 246–251 247 Fig. 1. Schematic of same and different trial displays. In the actual displays, the pictures were in color without labels and the rectangle was white all on a black background. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) for pigeons (∼10 s), intermediate for monkeys (∼30 s), and most slowly for humans (∼100 s). If list memory had been tested at one retention delay, then a likely conclusion would have been quali- tative differences in species’ visual list memory due to differences in primacy and recency effects. The results showing basically sim- ilar patterns of SPF changes with retention delay are the basis for concluding qualitative species similarity in visual list memory. The results showing different time-course differences among species are the basis for concluding quantitative species differences in visual list memory. One purpose of this article is to show qualitative similarity between pigeons, rhesus monkeys and capuchin monkeys in their functions relating abstract-concept learning to size of the train- ing set. Another purpose of this article is to show quantitative as well as qualitative similarity among these species. Pigeons will be shown to transfer to novel stimuli at a level equivalent to the mon- Fig. 2. Set-size functions of baseline and transfer performance for pigeons (blue), keys under conditions without detrimental carryover effects from rhesus monkeys (red), and capuchin monkeys (green) as their training sets were pro- prior training despite vastly different neural architectures and evo- gressively expanded from 8 items to 128 items (monkeys) or 1024 items (pigeons). lutionary histories. Although this is a special set of circumstances Error bars are standard errors of the mean. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) producing equivalent abstract-concept learning, it is a rare example (maybe unique in abstract-concept/rule learning) where pigeons show equivalent abstract-concept learning to monkeys—and two 2. Learning, transfer, abstract-concept learning, and monkey species in this case. qualitative similarity 1. Monkeys and pigeons trained and tested with an Learning rates on the initial 8-item task were similar for the expanding 8-item training set same/different training and 3 species—30-35 sessions. Following learning, a transfer test was testing procedures conducted. Test pictures on transfer trials were novel. Correct choices were rewarded as they were on baseline trials. Transfer Rhesus monkeys (3), capuchins monkeys (3), and pigeons tests consisted of 6 consecutive transfer test sessions (90 baseline (4) were trained and tested with expanding training-sets in a trials plus 10 intermixed transfer trials). The transfer tests follow- same/different (S/D) task. They were trained with the same items, ing 8-item set training showed little or no transfer for monkeys the same displays, the same choice responses, the same visual- or pigeons. As the training set was progressively doubled to 1024 angles of the displays, the same performance criteria, the same items, transfer increased for all species. degree of set-size expansions, and the same test items. Test cham- Fig. 2 shows transfer as a function of training set size. These bers employed video monitors and touch screens mounted flush in functional relationships provide a better comparison of abstract- the stimulus panels. Also