Annie E. Wertz

Selective Social Learning of Plant Edibility in 6- and 18-Month-Old Infants

Recent research underscores the importance of social learning to the development of food preferences. Here, we explore whether social information about edibility—an adult placing something in his or her mouth—can be selectively tied to certain types of entities. Given that humans have relied on gathered plant resources across evolutionary time, and given the costs of trial-and-error learning, we predicted that human infants may possess selective social learning strategies that rapidly identify edible plants. Evidence from studies with 6- and 18-month-olds demonstrated that infants selectively identify plants, over artifacts, as food sources after seeing the same food-relevant social information applied to both object types. These findings are the first evidence for content-specific social learning mechanisms that facilitate the identification of edible plant resources. Evolved learning mechanisms such as these have enabled humans to survive and thrive in varied and changing environments.

Thyme to touch: Infants possess strategies that protect them from dangers posed by plants

Plants have been central to human life as sources of food and raw materials for artifact construction over evolutionary time. But plants also have chemical and physical defenses (such as harmful toxins and thorns) that provide protection from herbivores. The presence of these defenses has shaped the behavioral strategies of non-human animals. Here we report evidence that human infants possess strategies that would serve to protect them from dangers posed by plants. Across two experiments, infants as young as eight months exhibit greater reluctance to manually explore plants compared to other entities. These results expand the growing literature showing that infants are sensitive to certain ancestrally recurrent dangers, and provide a basis for further exploration.

Categories and Constraints in Causal Perception

When object A moves adjacent to a stationary object, B, and in that instant A stops moving and B starts moving, people irresistibly see this as an event in which A causes B to move. Real-world causal collisions are subject to Newtonian constraints on the relative speed of B following the collision, but here we show that perceptual constraints on the relative speed of B (which align imprecisely with Newtonian principles) define two categories of causal events in perception. Using performance-based tasks, we show that triggering events, in which B moves noticeably faster than A, are treated as being categorically different from launching events, in which B does not move noticeably faster than A, and that these categories are unique to causal events (Experiments 1 and 2). Furthermore, we show that 7- to 9-month-old infants are sensitive to this distinction, which suggests that this boundary may be an early-developing component of causal perception (Experiment 3).

Theory of Mind in the Wild: Toward Tackling the Challenges of Everyday Mental State Reasoning

A complete understanding of the cognitive systems underwriting theory of mind (ToM) abilities requires articulating how mental state representations are generated and processed in everyday situations. Individuals rarely announce their intentions prior to acting, and actions are often consistent with multiple mental states. In order for ToM to operate effectively in such situations, mental state representations should be generated in response to certain actions, even when those actions occur in the presence of mental state content derived from other aspects of the situation. Results from three experiments with preschool children and adults demonstrate that mental state information is indeed generated based on an approach action cue in situations that contain competing mental state information. Further, the frequency with which participants produced or endorsed explanations that include mental states about an approached object decreased when the competing mental state information about a different object was made explicit. This set of experiments provides some of the first steps toward identifying the observable action cues that are used to generate mental state representations in everyday situations and offers insight into how both young children and adults processes multiple mental state representations.

Three-month-old-human infants use vocal cues of body size

Differences in vocal fundamental (F0) and average formant (Fn) frequencies covary with body size in most terrestrial mammals, such that larger organisms tend to produce lower frequency sounds than smaller organisms, both between species and also across different sex and life-stage morphs within species. Here we examined whether three-month-old human infants are sensitive to the relationship between body size and sound frequencies. Using a violation-of-expectation paradigm, we found that infants looked longer at stimuli inconsistent with the relationship—that is, a smaller organism producing lower frequency sounds, and a larger organism producing higher frequency sounds—than at stimuli that were consistent with it. This effect was stronger for fundamental frequency than it was for average formant frequency. These results suggest that by three months of age, human infants are already sensitive to the biologically relevant covariation between vocalization frequencies and visual cues to body size. This ability may be a consequence of developmental adaptations for building a phenotype capable of identifying and representing an organisms size, sex and life-stage.

Pathways to cognitive design

Despite a shared recognition that the design of the human mind and the design of human culture are tightly linked, researchers in the evolutionary social sciences tend to specialize in understanding one at the expense of the other. The disciplinary boundaries roughly correspond to research traditions that focus more on natural selection and those that focus more on cultural evolution. In this paper, we articulate how two research traditions within the evolutionary social sciences-evolutionary psychology and cultural evolution-approach the study of design. We focus our analysis on the design of cognitive mechanisms that are the result of the interplay of genetic and cultural evolution. We aim to show how the approaches of these two research traditions can complement each other, and provide a framework for developing a wider range of testable hypotheses about cognitive design. To do so, we provide concrete illustrations of how this integrated approach can be used to interrogate cognitive design using examples from our own work on plant and symbolic group boundary cognition. We hope this recognition of different pathways to design will broaden the hypothesis space in the evolutionary social sciences and encourage methodological pluralism in the investigation of the mind.

The principles of object continuity and solidity in adult vision: Some discrepancies in performance.

Infant looking-time results (Spelke, 1994) have shown that pre-verbal infants grasp the continuity principle (i.e. that objects cannot pop in and out of existence) and the solidity principle (i.e. that solid objects cannot pass through one-another) from around 3 months of age. Early theories assimilated both by treating solidity as resulting from a single, general principle of object continuity. However, more recent work on primates and older children (Santos, 2004; Keen, 2003) has suggested that children and primates have a greater mastery over continuity than solidity in action-based tasks. One potential explanation for this is that the vision/action system places a higher priority on continuity than solidity in object tracking. Here we tested this hypothesis directly using a novel object detection task. Adult participants viewed short videos depicting an object rolling behind one or two occluding screens. The occluding screen(s) then dropped, revealing the ball in a location either indicative of a continuity/solidity violation or non-violation, and participants were required to indicate the location in which they perceived the ball via keypress within 750ms. Participants were tested in one of two learning conditions: a 75% non-violation condition or a 75% violation condition. Across three experiments, we observed (consistent with our original hypothesis): (1) A larger decrease in accuracy for violations relative to non-violations in the continuity than solidity condition. (2) A consistent three-way interaction between learning condition, physical principle (solidity vs. continuity), and violation. This three-way interaction resulted from the fact that in the 75% violation condition, participants learned to overturn solidity but not continuity based anticipations. Taken together these findings suggest that the visual system indeed places a higher priority on object continuity than solidity, and so offer a potential explanation for some puzzling developmental results. Meeting abstract presented at VSS 2015.