Preheat the oven to 425 degrees F. Line a baking sheet with parchment paper. Place the cream cheese in large a bowl and beat with an electric mixer until smooth and lightened. Mix in the garlic, cayenne, chopped artichoke hearts, chopped chives or dill, salt, white pepper and lemon juice. Spread the mixture on the bread slices and place on the baking sheet. Place 2 or 3 shrimp on the top of each melt and then sprinkle with the parmesan cheese. Bake for 10 to 12 minutes, or until light golden on top. Arrange on a serving platter, garnish each melt with a dill sprig or slice of chive and serve.