People are slower at responding to tactile stimuli than to input from the other senses. It's not immediately obvious why this should be. It's unlikely to be for mechanical reasons: the retina in the eye is slower at converting input into a neural signal than is the skin. Psychologists think the answer may have to with attention. Perhaps we're not so good at keeping our attention focused on the tactile modality compared with the others. Now Louise Connell and Dermot Lynott have added to the picture by showing that the tactile disadvantage extends to the conceptual domain. That is, we seem to be slower at recognising when a word is tactile in nature than we are at recognising whether words are visual, to do with taste, sound, or smell.
The researchers had dozens of participants look at words on a screen, presented one at a time, and press a button to say if they were related to the tactile modality (e.g. 'itchy') or not. Some words were tactile-related whilst others were fillers and related to the other senses.
The same task was then repeated but with participants judging whether the words were visual-related, auditory and so on, with each sense dealt with by a new block of trials. The key finding is that participants were much slower at this task in the tactile condition than for the other senses. This was the case even when words were presented for just 17ms, which is too fast for conscious detection but long enough for accurate responding.
To make sure the slower performance in the tactile condition wasn't to do with the response requiring a button press (which inevitably causes tactile stimulation), the researchers repeated the experiment with vocal responding via a microphone. The results were pretty much the same.
Ensuring they left no stone unturned, Connell and Lynott also conducted a final experiment to check that there isn't something about tactile words, besides their touchiness, that makes them slower to process. To do this they used words that have both visual and tactile qualities - examples include shaggy and spiky - and they mixed these in among filler words that related to the other senses. The same words were used in the tactile condition (in which participants had to say whether each word was tactile-related or not) and a visual condition. Once again, participants were significantly slower in the tactile condition.
Connell and Lynott say their findings provide further evidence for the tactile sense having a processing disadvantage relative to the other senses. They think this is because there's little evolutionary advantage to sustaining attention to the tactile modality whereas there are obvious survival advantages with the other senses, for example: '...in hunting, where efficacious looking, listening and even smelling for traces of prey could afford an advantage.' You may think of pain and damage detection as reasons for paying sustained attention to the tactile domain, but remember these are served by spinal reflexes. 'We do not wait for the burning or stinging sensation to register with the attentional system before responding,' the researchers said.
Connell L, & Lynott D (2010). Look but don't touch: Tactile disadvantage in processing modality-specific words. Cognition, 115 (1), 1-9 PMID: 19903564
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.