Emily D. Klein, PhD

 

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Current Research
Much of my research in graduate school focused on learning mechanisms and cognition using avian and rodent models. As a postdoctoral researcher at the Language Research Center I am hoping to expand my research repertoire and shift my focus to primate cognition. In particular, I am interested in social learning, memory strategies, and relational learning.

 

Research with Thomas Zentall, University of Kentucky

My graduate research experience began in Dr. Thomas Zentall's laboratory at the University of Kentucky. One of my first projects in Dr. Zentall's lab was running a series of experiments exploring the imitative ability of Japanese quail and pigeons while controlling for affordance learning (learning about the properties and uses of an object). We found that both quail and pigeons are able to imitate a demonstrator that pushes a sliding screen to the left or to the right of a feeder opening. Additionally, it was found that pigeons could benefit from affordance learning (watching the screen move) in the absence (but not the presence) of a non-performing demonstrator. This latter project became my master's thesis. A more recent imitation experiment found that pigeons were able to imitate a demonstrator performing a two-action sequence (pecking or stepping on a treadle and then sliding a screen either to the left or to the right of a feeder opening). To my knowledge this is the first evidence of two-action sequence imitation in nonhuman animals other than chimpanzees.

Another line of research I have explored relates to how pigeons code long (10-s) versus short (2-s & 0-s) samples over increasing delays. It has been hypothesized that the memory for time becomes subjectively shorter as delays increase. Thus, over longer delays a 10-s sample appears more like a 2-s sample and a 2-s sample seems more like a 0-s sample. However, in a series of experiments we were able to show that the subjective shortening effect is an artifact of the traditional experimental design. Specifically, we found that pigeons confuse the intertrial interval (ITI) with the novel test delays and are thus biased to respond to samples as if they were absent (e.g. short). When the ITI and the delay are made distinct (achieved by lighting the ITI), the subjective shortening effect disappears. Two follow-up experiments using 3 non-zero times (2, 8, and 32-s) found suggest that pigeons have considerable flexibility in the development of coding strategies and support earlier evidence that under appropriate conditions pigeons can develop a single-code/default coding strategy in the absence of event ambiguity or the use of an absent event.

I have explored whether humans prefer stimuli that signals reward when it follows high versus low effort. Specifically, we found that human participants prefer shapes that follow high effort (making 20-30 mouse clicks) over shapes that follow low effort (1 mouse click). These results suggest that the effort exerted to obtain a reward can actually increase its subjective value. Similar results have been found with pigeons. I am now using pigeons to investigate specific factors that may mediate this effect by asking whether previous work history (easy or challenging) influences the perceived shift in subjective value.

 

Research with Michael Bardo, University of Kentucky

While at the University of Kentucky I also worked with Dr. Michael Bardo running a series of experiments that investigated the motivational and behavioral differences in enriched- and isolate-reared rats. We found that there were no significant differences in free consumption of sucrose or standard rat chow in rats regardless of rearing environment and regardless of whether they were on a free-feed or restricted food schedule. The lack of difference in consumption is important because previous experiments had found significant differences in lever pressing for sucrose, with isolate-reared rats exhibiting higher breakpoints and faster latencies to complete sessions than enriched rats. Thus it appears that isolated rats are more motivated than enriched rats to work for sucrose, even though both groups are equally motivated to consume sucrose.

In a follow-up study, also with differentially reared rats, we investigated acquisition, maintenance, extinction, and reinstatement of sucrose-reinforced operant responding. Although we found no differences in acquisition and maintenance, we did find that enriched rats extinguished faster and more completely compared to isolated rats. Additionally, when presented with a noncontingent sucrose prime (either 1-pellet or 10-pellets, counterbalanced for order of presentation) both groups of rats reinstated responding, but only enriched rats reinstated differentially. Specifically, enriched rats increased responding to the previously active lever and responded more to the 10-pellet prime (compared with the 1-pellet prime). Isolated rats reinstated equally to both the active and inactive levers regardless of prime magnitude. Most recently, I investigated whether rearing environment affected impulsive behavior. Using a delayed reward discounting task, I found that adult rats reared in an enriched condition (but in standard housing at the time of the experiment) were significantly less impulsive than isolate-reared rats (also in standard housing at the time of the experiment).

Finally, my dissertation explored whether chronic exposure to cocaine would cross-sensitize rats to sucrose. I found that rats sensitized to cocaine (but in a drug-free state at the time of testing) showed increased motivation to obtain sucrose reward. Specifically, cocaine-sensitized rats demonstrated enhanced sucrose-induced place preference and demonstrated higher P.R. break-points with saline controls. This result is interesting because I also found that cocaine-sensitized rats consumed less freely available sucrose than saline controls. Taken together these results indicate that cocaine sensitization increases sucrose seeking (searching for sucrose) but not sucrose liking.