Responses to partners overcall of 1♥ or 1♠ (1 in a major)
An overcall with 1♥ or 1♠ can be made on hands with a very wide point range, from 8 to 17HCP and the responses are subject to these limits. With 8-11 HCP, the appropriateness of an overcall depends on three criteria: vulnerability, distribution and suit quality. Three objectives are associated with these conditions: to hinder the opposition, to suggest a sacrifice or to suggest a lead. With 12HCP+ the only condition is to have a five-card suit, your objective being to declare a contract.
Very helpful. Need to study this to help me raise the bar on my game!