What you might not know, however, is just how much meaning they're actually missing when you verbally communicate with them. New research suggests dogs might be missing more than we realise.
Despite dogs' excellent hearing and ability to analyse and process different speech sounds, a new study led by researchers at Eötvös Loránd University, Budapest indicates that even minor differences may be missed by dogs, who fail to distinguish subtle variances between similar-sounding words.
"While dogs have remarkable abilities for social cognition and communication, the number of words they learn to recognise typically remains very low," the researchers explain in their paper.
"The reason for this limited capacity is still unclear."
To probe these limitations in dogs' auditory vocabulary (if you will), the researchers conducted an experiment, in which over 40 dogs were brought into the lab, having their brain activity measured non-invasively via electroencephalography (EEG) electrodes attached to their scalp.
While connected to the equipment, the animals heard three different types of words spoken on a recording: familiar instruction words (eg. 'sit'), phonetically similar nonsense words (eg. 'sut'), and dissimilar nonsense words (eg. 'bep').
The EEG results, based on a subset of 17 animals whose data were considered reliable, showed a clear difference in the dogs' brain responses – called event-related potentials (ERPs) – when they heard either familiar words or the dissimilar-sounding nonsense words.
On the whole, though, the ERPs suggested dogs weren't able to distinguish between the familiar instructions (such as 'sit') and similar-sounding nonsensical terms (such as 'sut'), given the phonetic overlap between them.
The researchers hypothesise that the limitation is not due to insufficient perceptual discrimination – as dogs have previously been capable of identifying subtle changes in human speech sounds – but could reflect something about how the animals focus their attention.
Young infants, the researchers note, also fail to discriminate between very similar-sounding words when they are very young (younger than 14 months), but later learn to distinguish slight changes in phonetics, which is what underlies the human ability to possess large vocabularies.
For whatever reason – which future research might be able to elucidate – it seems dogs don't get past that hurdle, failing to pay attention to all of the speech sounds that make up words.
This might be a factor in why dogs tend to learn only a limited amount of human words, but it also could mean that they don't understand humans as much as humans might think: Similar-sounding words could be tripping them up, being perceived in their brains as the same thing.
"Similarly to the case of human infants, we speculate that the similarity of dogs' brain activity for instruction words they know and for similar nonsense words reflects not perceptual constraints but attentional and processing biases," senior researcher Attila Andics explains.
"Dogs might not attend to all details of speech sound when they listen to words."
The findings are reported in Royal Society Open Science.