Three animals (F3, F6, G13) developed high levels of accuracy and showed rapid acquisition during baseline sessions. Three animals (F3, F6, G13) have shown high levels of accuracy during novel probes and four (F3, F6, G13, G8) during novel stimulus combinations. Impressively, these accurate performances occurred despite highly variable spatial configurations of stimuli (18 different positions) made possible by the arena apparatus. Performance during Novel Probes and Combinations appears to improve across exemplars of the identity relation. Number of sessions to criterion during baseline stimulus sets decreases as a function of training. One animal (G8) is currently in advanced Identity MTS training and testing phases and beginning to show evidence of accurate matching during novel probes and combinations. One animal (H8) acquired only one baseline discrimination (set A), and completed only one Probe phase (set B,C,D). While individual differences are apparent, some subjects have rapidly learned the MTS discriminations and transferred responding to novel stimuli - providing evidence of generalized MTS with olfactory stimuli and systematic replication of Peňa et al. (2006). Currently, the most advanced subjects (F3, F6, G13) are being further tested for more complex relations (arbitrary MTS, stimulus equivalence). The contribution of class-consistent reinforcement (sucrose or sucrose/grain pellets) on class formation and equivalence relations is also being evaluated in these on-going, advanced stages. MTS Procedures Subjects were presented a sample stimulus followed by multiple comparison stimuli. Responses to the comparison (S+) identical to the sample were always reinforced; responses to the dissimilar comparison (S-) were never reinforced. Responses were defined as any displacement of the lid from the cup rim using the front paws, snout, or face. After lid removal, subjects were required to dig in the scented sand to retrieve buried reinforcers. A correction procedure was used; trials continued until a response to S+ occurred. S+, S- locations were varied pseudorandomly First set (A) - 2 different olfactory stimuli All other sets - 6 stimuli (3 from each class) Stimulus classes (A1-S1 and A2-S2) were established for use in later phases (e.g. equivalence testing). Following criterion performance (2 consecutive days at ≥ 90%) on a set, Novel Probes were conducted. Generalized MTS was tested via probe sessions conducted during the first session with novel stimuli. Novel Probes: first 6 trials when novel stimuli serve as samples. To ensure control of responding by stimulus odor, and not pellet odor, probes were not baited (reinforcers were delivered after response to S+). Novel Combinations: later trials within the first session of a set, with novel sample-comparison stimulus combinations. Occasional inter-rater reliability sessions were conducted and high levels of observer agreement were found (98% agreement on 128 trials). References Iversen, I.H. (1993). Acquisition of matching-to-sample performance in rats using visual stimuli on nose keys. Journal of the Experimental Analysis of Behavior, 59, Iversen, I.H. (1997). Matching-to-sample performance in rats: A case of mistaken identity? Journal of the Experimental Analysis of Behavior, 68, Peňa, T., Pitts, R., & Galizio, M. (2006). Olfactory Identity Matching in the Rat Using Olfactory Stimuli. Journal of the Experimental Analysis of Behavior, 5, Introduction Emergence of generalized identity matching-to- sample (MTS) was evaluated in rats using olfactory stimuli and multiple exemplars in an open-field apparatus. Generalized identity MTS is often used to study concept learning. With the exception of Peňa, Pitts, & Galizio (2006), generalized identity MTS has been difficult to demonstrate in rats (Iversen, 1993 & 1997). Olfactory stimuli may have contributed to the success of Peňa et al. (2006). The current study replicated Peňa et al. (2006) using the same olfactory discrimination procedure wherein subjects are trained to dig in scented sand to obtain pellet reinforcers. A different version of multiple exemplar training was used to train subjects the identity relation. The open-field arena apparatus, unlike the modified operant chamber used in Peňa et al. (2006), varied spatial locations of comparisons and may facilitate control by the stimuli. Contact information: Methods Five male, HSD rats were trained to remove perforated lids and dig in cups of scented sand to obtain pellet reinforcers using shaping procedures. Perforated plastic lids were placed on top of the stimulus cup rim. Stimuli were mixed using a 10g spice/1000g sand ratio. Subjects were trained the MTS relation and tested for generalized matching in the open-field arena apparatus. 2 circular arrays, numbered clockwise 94cm diameter, 18 5cm holes, 13cm apart Conclusions and Future Directions Evaluating Olfactory Identity Matching-To-Sample (MTS) in Rats Using an Open-field Apparatus Poerstel, L. B. Bullard, L. A., Rayburn-Reeves, R. M., Weiland, K., Bruce, K. E., & Galizio, M. University of North Carolina - Wilmington Figure 1. Percent Correct for individual sessions across stimulus presentations. Panel labels denote stimulus sets, horizontal line indicates criterion, vertical denotes phase change. Fractions are correct responses during Novel Probes (first 6 Novel trials of the first session of a set where novel stimuli serve as samples) over total possible (6). Percentages indicate percent correct for Novel Combinations (trials within first session of a set, after Novel Probes, with novel sample-comparison stimulus combinations). Sample Stimulus Arrangement - Subject F3 Set 1: A1 NutmegA2 Dill Set 2: B1 CeleryB2 Cinnamon C1 CloveC2 Ginger D1 OreganoD2 Onion Set 3: E1 ThymeE2 Coriander F1 MustardF2 Sumac G1 CuminG2 Marjoram Set 4: H1 GarlicH2 Rosemary I1 SageI2 Turmeric J1 BayJ2 Paprika Set 5: K1 SassafrasK2 Hickory L1 WorcestershireL2 Orange M1 SavoryM2 Fennel Set 6: N1 CarobN2 Allspice O1 BeetO2 Caraway P1 LimeP2 Tomato Percent Correct for Consecutive Sessions Across Stimulus Set Presentations Percent Correct (%) Consecutive Sessions Summary Across Novel Probe and Novel Combination Probe Conditions for Individual Subjects Figure 2. Average performance for each subject during all Novel Probes compared to the last two Novel Probes, and all Novel Combinations compared to the last two Novel Combinations. Horizontal line indicates chance performance.