Is numerosity an abstraction that arises downstream of basic perceptual processing, or does the brain process numerosity like a primary perceptual feature such as color or motion? Here, we tested whether visual cortex computes number automatically, even when number is task-irrelevant and is being processed unconsciously. We recorded electroencephalography while subjects watched dotcloud stimuli that alternated in numerical content at 15 Hz, under one of three conditions: judging numerosity, judging convex hull, or making no judgments. Under all three conditions, we observed oscillatory activity at 15 Hz in early visual cortex. The strength of this signal depended on the numerical content of the stimuli in all three conditions and did not differ significantly across the conditions. Results show that number can be computed spontaneously by visual cortex, even when participants are attending to non-numerical information, consistent with the proposal that number is a primary perceptual attribute of visual stimuli.

When people understand language about their own actions they activate premotor regions they use to perform these actions.Do people understand language about other peoples actions by imagining how they perform these actions themselves, orhow they perceive others performing them? Here, we recorded BOLD fMRI while left- and right-handers read about andthen imagined their own unimanual actions (e.g. you write) or others actions (e.g. she writes). When imagining theirown manual actions, participants preferentially activated PMC circuits controlling their dominant hand. By contrast, whenimagining others actions, participants PMC activity reflected both how they perform actions themselves and how theytypically see actions performed by right-handers (about 90% of people they see). Language-induced motor imagery forour own actions reflects how we use our own bodies, whereas imagery for others actions also reflects how others use theirbodies, even if their bodies differ from our own.

How do humans compute approximate number? According to one influential theory, approximate number representationsarise in the intraparietal sulcus and are amodal (independent of any sensory modality). Alternatively, approximate numbermay be computed initially within sensory systems. We tested for approximate number representations in the visual systemusing steady state visual evoked potentials (SSVEPs). We recorded EEG from human subjects while they viewed dotcloudspresented at 30 Hz. Alternating the dotcloud numerosity at 15 Hz evoked a 15 Hz SSVEP detectable over the occipital lobe(Oz). The SSVEP amplitude increased as the numerical difference between dotclouds increased, indicating that subjectsvisual systems were differentiating dotclouds on the basis of their numerical ratios. Critically, subjects were unable toconsciously discriminate dotcloud numerosity, indicating the rapid presentation disrupted reentrant feedback to visualcortex. Approximate number appears to be computed within the visual system, independently of higher-order areas suchas the intraparietal sulcus.