Why is speech invariance a potential problem for the listener?

CHOOSE TWO QUESTIONS AND ANSWER THEM (each answer should be about 750 words)

1. Why is speech invariance a potential problem for the listener?
2. How and why do psycholinguists distinguish between lexical access and word recognition?
3. Choose one model of speech recognition and explain and exemplify its core elements.
4. Outline some of the experimental tests that have been carried out on The Cohort Model. Comment on their consequences for the reliability of the model