Language boosts invisible objects into visual awareness

New research suggests that language can both enhance and diminish the sensitivity of our vision
Misty dawn Misty dawn at Loch Voil in Perthshire. Photograph: Adam Burton/Getty Images

The philosopher Ludwig Wittgenstein famously said that, "the limits of my language mean the limits of my world," meaning that we can only understand the world through the language we use, and that if our language does not include words for some particular idea or concept, then that concept cannot exist for us. The relationship between language and thought is complex, which researchers continue to debate. Some, like Wittgenstein, argue that thought is dependent on language. Others point out that thought can occur in the absence of language, deaf people being an important case in point.

These arguments focus on the relationship between language and so-called "higher order" thought processes – our ability to evaluate and analyse, to conceptualise and understand. What about lower-order brain mechanisms, such as perception? New research provides evidence that language can influence these processes, so that hearing the name of an otherwise invisible object can enhance visual perception, boosting that object into our conscious awareness.

One school of thought that became popular during the 1980s states that the brain contains "modules", or processing streams, that do not influence each other. Accordingly, vision and language are distinct, and the contents of visual perception are impenetrable to external influences such as sounds and words. There is, however, a growing body of evidence that suggests otherwise. For example, a brief sound heard at the right time can make us perceive moving objects as bouncing off each other instead of moving together; a single flash of light can be perceived as multiple flashes when accompanied by multiple beeping sounds; and contextual cues can influence the way we perceive faces.

These experiments show that sound can have subtle effects on certain qualities of visual experience, but do not provide evidence that language can directly influence visual awareness. Gary Lupyan of the University of Wisonsin-Madison and Emily Ward, now a PhD student at Yale, therefore designed a series of experiments to test the idea that language modulates visual perception, to bring an otherwise invisible object into visual awareness.

They recruited university students and, using a special piece of equipment, presented them with images of familiar objects into one eye for a few seconds each, while simultaneously presenting a flashing light into the other. The flashing light effectively suppresses the pictures for extended periods of time, rendering them invisible. Hearing the name of the object just before it was presented significantly improved their performance, making them far more likely to say that they had just seen the object, and to do so quicker, than when they didn't hear the name of the object. On the other hand, hearing a word that did not match the object they were about to see worsened their performance, making them less likely to report seeing the object than when the pictures were shown without their labels.

Lupyan and Ward conclude that language can enhance the sensitivity of visual awareness, making their participants able to detect objects that would otherwise have been hidden from view, and that this effect occurs at the earliest stages of perceptual processing, rather than at later stages corresponding to "higher" thought processes. They also propose two possible mechanisms by which this might occur. Hearing the name of the object might give the visual brain areas a head-start, so that neurons in those areas that are selective for that particular object have a competitive edge over those that respond to other objects. Alternatively, hearing object names might activate complex neural representations of a given object, which then facilitates its detection.

The researchers favour the first explanation, because earlier work suggests that the method used to suppress the images interferes with visual processes that occur before the brain can analyse the meaning of words. Regardless of how it happens, the results clearly show that language and vision can interact to influence behaviour. Given that the purpose of vision is to create a model of the world, couldn't such sensitivity to language be a disadvantage? Lupyan and Ward say it doesn't, and suggest these interactions might in fact be a useful adaptation to how the visual system works.

They point out that visual perception involves making inferences from incomplete information. Most of the objects we see are at least partially hidden from view, but the brain automatically fills in the gaps to make a best guess about what it is we're seeing at any given moment. (Kanizsa's triangle, which creates illusory contours, demonstrates this nicely; how might hearing different shape names affect how it's perceived?) Thus, they argue, "perception needs all of the help it can get" from other brain systems, including from language, which can tune the visual system to make it more sensitive to things that are relevant to the task at hand.

Reference: Lupyan, G. & Ward, E. J. (2013). Language can boost otherwise unseen objects into visual awareness. PNAS, DOI: 10.1073/pnas.1303312110

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