Kant argued that Euclidean geometry is synthesized on the basis of an a priori intuition of space. This proposal inspired much behavioral research probing whether spatial navigation in humans and animals conforms to the predictions of Euclidean geometry. However, Euclidean geometry also includes concepts that transcend the perceptible, such as objects that are infinitely small or infinitely large, or statements of necessity and impossibility. We tested the hypothesis that certain aspects of nonperceptible Euclidian geometry map onto intuitions of space that (...) are present in all humans, even in the absence of formal mathematical education. Our tests probed intuitions of points, lines, and surfaces in participants from an indigene group in the Amazon, the Mundurucu, as well as adults and age-matched children controls from the United States and France and younger US children without education in geometry. The responses of Mundurucu adults and children converged with that of mathematically educated adults and children and revealed an intuitive understanding of essential properties of Euclidean geometry. For instance, on a surface described to them as perfectly planar, the Mundurucu's estimations of the internal angles of triangles added up to ∼180 degrees, and when asked explicitly, they stated that there exists one single parallel line to any given line through a given point. These intuitions were also partially in place in the group of younger US participants. We conclude that, during childhood, humans develop geometrical intuitions that spontaneously accord with the principles of Euclidean geometry, even in the absence of training in mathematics. (shrink)

Is calculation possible without language? Or is the human ability for arithmetic dependent on the language faculty? To clarify the relation between language and arithmetic, we studied numerical cognition in speakers of Mundurukú, an Amazonian language with a very small lexicon of number words. Although the Mundurukú lack words for numbers beyond 5, they are able to compare and add large approximate numbers that are far beyond their naming range. However, they fail in exact arithmetic with numbers larger than 4 (...) or 5. Our results imply a distinction between a nonverbal system of number approximation and a language-based counting system for exact number and arithmetic. (shrink)

Humans, being highly social creatures, rely heavily on the ability to perceive what others are doing and to infer from gestures and expressions what others may be intending to do. These perceptual skills are easily mastered by most, but not all, people, in large part because human action readily communicates intentions and feelings. In recent years, remarkable advances have been made in our understanding of the visual, motoric, and affective influences on perception of human action, as well as in the (...) elucidation of the neural concomitants of perception of human action. This article reviews those advances and, where possible, draws links among those findings.Acronyms and DefinitionsApparent motion: perception of smooth motion from brief, successive exposures of static imagesChameleon effect: tendency for people to mimic the actions of others without even knowing itCommon coding principle: theory that perceiving and acting share common mental representationsDynamic noise: an array of randomly positioned dots that can camouflage perception of PL animations when the noise dots are sufficiently denseEvent-related potential : electrical brain activity registered from the scalpExtrastriate body area : brain region activated when a person views a human body or body partsFunctional magnetic resonance imaging : widely used technique that reveals brain activation patterns based on hemodynamic responses to neural activityInversion effect: difficulty of perceiving PL animations when they are shown upside downKinematics: analysis of the motions of objects without regard to the forces producing themMirror neurons: brain cells responsive when an animal engages in an activity or when it watches another animal engaged in that activityPoint-light animations: biological activity portrayed by small light tokens placed on the major body parts of an actorPositron emission tomography : brain imaging technique that uses radioactively labeled tracers to allow visualization of active brain areasSpatiotemporal jitter: means of degrading perception of PL animations, where the relative timing and positions of the moving dots are perturbedSuperior temporal sulcus : region of the cortex the posterior portion of which contains neurons selectively responsive to human activityTemplate-matching model: theory that perception of biological motion results from concatenation of static views of the bodyTranscranial magnetic stimulation : technique producing a brief disruption of neural processing. (shrink)