Visual memory for novel shapes: implicit coding without attention.

Implicit memory for novel shapes was explored with a negative priming paradigm. The results show that representations of shapes, formed in a single trial and without attention, can last without decrement across 200 intervening trials and with temporal delays of up to a month. No explicit memory of the shapes was available, either immediately or after a delay. There were consistent individual differences in the amount of negative priming shown, and some participants showed only facilitation. There was a trend toward increased facilitation across time, as if the memory of the shape survived longer than an "action tag" attached to it, which specified whether it should be attended or ignored. The results demonstrate a surprising combination of plasticity and permanence in the visual system and suggest that the roles of both attention and repetition may be to ensure voluntary retrievability rather than to form a lasting memory.