Towards a better understanding of explicit-declarative learning in humans and non-human primates

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

Learning and memory are crucial to every aspect of education, intellectual functioning, and daily living. Researchers who study memory have definitively shown that there are different systems of memory (e.g., unconscious habit memory vs. conscious declarative memory). This knowledge has changed society’s views of cognitive aging, dementia, and amnesia.

However, researchers who study the basic mechanisms of learning have not participated in this systems revolution, and this is a barrier to scientific progress. For example, there might be different systems of learning that have different strengths, uses, brain organizations, cognitive-developmental trajectories, and levels of preservation during cognitive aging.

But such differentiations cannot be clearly made while the dominant mode of thinking in the learning literature preserves an emphasis on a unitary learning system. Accordingly, this project brings to the domain of learning research the separation between implicit-behavioral learning (i.e., learning to react automatically, habitually, unconsciously) and explicit-declarative learning (i.e., learning new knowledge conceptually, consciously, perhaps verbalizably).

The project uses innovative methods toward this end. These methods selectively suppress implicit learning, defeating habit-based learning that can interfere with explicit forms of learning, and therefore selectively fostering explicit learning. These methods fill important gaps in the learning literature.

Applying them across humans and nonhuman primates has the potential to transform comparative psychology by opening a new window on animals’ reflective minds, and possibly providing illuminating insights into animal consciousness. The insights gained will also let researchers ask what contribution the use of language brings to explicit learning processes —an age-old question.

For example: Are human rules and hypotheses necessarily couched in language, or only conveniently so? Is it possible to wordlessly conceive of abstract relations between things? Is developing language why young children slowly achieve mature analogical reasoning?

Thus, this research will provide paradigms perfectly suited to future researchers studying the earliest manifestations of explicit learning in young children. New methods to foster explicit learning could help children with developmental delay, learning disabilities, and autism spectrum disorder—by teaching them basic approaches to that learning that are less language-bound or less introspective and self-conscious.

The methods could let educators focus students’ learning effort toward the explicit/conceptual level and optimize their success. The research will produce animal models of explicit learning to further the neuro-scientific study of explicit cognition, revealing its brain organization, pointing to factors that may reduce its functionality and factors that may enhance it.

Thus, the project bears on the evolution of humans’ highest cognitive capacities—an important part of the story of human emergence.

Myriad human and animal learning studies have provided subjects with immediate, concrete, trial-by-trial reinforcement. This approach limits scientific understanding because it allows low-level forms of automated, habitual learning to control the learning process. In turn, this can interfere with the operation of higher-level forms of explicit-conceptual learning that may be more desirable.

Accordingly, this project uses alternative reinforcement environments—that is, displaced reinforcement—to surmount this obstacle and achieve its ends. For example, one method will ask participants to complete a block of trials before receiving any feedback. The project will show that displaced reinforcement defeats the processes of implicit-procedural learning, while encouraging participants to think explicitly and conceptually about the task at hand.

It will show that participants must self-supervise their learning in this reinforcement environment, relating the summary feedback to their self-discovered rule or strategy. Indeed, the crucial innovation of this project is that these effects operate synergistically, for with implicit-procedural learning selectively disabled, the investigators can observe a pivot to some other learning strategy such as the use of the explicit-declarative learning system.

Thus, the investigators are observing conscious hypotheses and rules, conceptual knowledge, and analogical relationships particularly enhanced. Specifically, Experiment 1 (E1) trains humans and animals to thrive in the altered reinforcement environments used in the research, a key preliminary grounding later experiments. E2 shows that displaced reinforcement selectively fosters the learning of rules based on single dimensions (e.g., big things are A; small things are B) that is typical of pre-frontal brain regions.

E3 asks whether a hypothesis-testing form of learning is selectively preserved under displaced reinforcement. E4 asks whether explicit learning under displaced reinforcement features conscious rule discovery and sudden learning (so-called “AHA experiences”). This may be a revolutionary finding about animal minds.

E5 demonstrates that participants can self-supervise their own learning under displaced reinforcement, applying their own conceptual framework. E6 lets monkeys – for the first time, without having ever received immediate reinforcement -- declare their own conceptual rules and category boundaries. The later experiments demonstrate that explicit-declarative learning is distinctive for fostering knowledge that is more generalizable and more conceptual.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.