By this view acess to episodic memories rapidly degrades and most are lost within 24h of formation. Only those episodic memories that integrated at the time or consolidated later, possibly during the sleep period following formation, remain accessible and can enter into the subsequent formation of autobiographical memories. Episodic memories are represented in the brain regions most closely involved in the processing that took place during actual experinece. Because of this episodic memory sensory-perceptual details are represented in posterior regions of the brain and especially in networks sited in the occipital lobes, posterior parts of the temporal lobes. Thus, Episodic memory is a topographically separate memory system. Episodic memories represent knowledge of specific actions and action autcomes derived from moment-by-moment experience. Tulving proposed that there is a distinction between episodic memory and semantic memory. Accordin to Tulving, as has already been explained, episodic memory refers to the storage and retrieval of specific events occurring at particular time in particular place. Retrieval mode is characterized by turning inwards of attention, a redirecting of attention from action to mental representations and, as a consequence, can probably only be engaged in under certain circumstances.