Does sustainability marketing make people think food is healthier? A systematic review of health halo effects.

The predictive coding theory of cortical function, proposed in this journal in 1999 by the author and Ballard, has been the subject of increasing attention in recent years. However, as originally proposed, the theory ignored a fundamental aspect of perception, namely, that perception is action based: we move our eyes about three times a second to recognize objects in a scene, orient our heads to localize sounds, use our fingers to identify objects by touch and navigate ourselves in our environment to solve tasks that satisfy our needs. Away from experimentally imposed constraints in the laboratory, perception, in its natural state, can best be viewed as an action-based hypothesis-testing process (also called active sensing, active perception and active inference). Recent studies have highlighted the important influence of impending actions across almost all cortical areas (). For example, in mice solving a visual discrimination task using forepaws to rotate a wheel, Zatka-Haas et al. observed, using widefield calcium imaging, extensive bilateral activity across cortical areas preceding movements on choice trials (left or right action selected) but not on ‘NoGo’ trials (no action is selected) (, left). They further showed that impending movement could be decoded from cortical activity in most imaged regions by 25 ms before movement (, right). In the same task, Steinmetz et al. used Neuropixels probes to record spiking activity from thousands of neurons and showed that, not only does activity in the visual cortex get updated after movement (, left), but almost all recorded cortical areas had neurons with activities that were predictive of upcoming movements (, right). Similarly, Stringer et al. found that about a third of the population activity of ~10,000 neurons in the visual cortex of awake mice could be predicted from motor actions derived from a video of the mouse’s facial movements (), suggesting that sensory–motor integration occurs even in the primary sensory cortex (the lack of a similar result in monkeys could be due to the increased functional specialization of primate visual cortical areas compared to that of the rodent cortex). Actions may be integrated differently across the different layers of a cortical area. For example, Jordan and Keller showed that both layer 2/3 and layer 5/6 neurons in the mouse primary visual cortex (V1) undergo depolarization before locomotion onset (, left and middle). While layer 2/3 neurons appear to be computing a difference between motor-related input and bottom–up visual flow input, layer 5/6 responses were consistent with positive integration of visuomotor inputs (, right). These results complement well-known earlier results on predictive activity in a range of cortical areas such as the visual cortex, the parietal cortex and frontal eye fields that anticipate the visual consequences of impending eye movements.