The McGurk Effect. The McGurk effect (named after Harry McGurk of McGurk & McDonald, 1976) is a compelling demonstration of how we all use visual speech information. The effect shows that we can't help but integrate visual speech into what we 'hear'. Try the demonstration now, and then read about how the stimuli were made, what the effect means, and how to produce your own McGurk effects. Instructions: You will see and hear a mouth speaking four syllables.