Toss together berries in a large bowl. Stir together sugar and extract, and sprinkle over berries, tossing to coat. Cover and chill 1 hour.
Prepare cake mix according to package directions.
Place paper baking cups in muffin pans; spoon batter into cups, filling two-thirds full.
Bake, 1 muffin pan at a time, at 350° for 15 minutes or until lightly browned. Remove cupcakes from pans to wire racks; cool.
Cut cupcakes in half horizontally; spoon 1 tablespoon berry mixture on bottom halves, and cover with tops. Spoon 1 tablespoon berry mixture on top halves, and dollop with whipped topping. Serve immediately.