Visual and auditory memory are both different categories of the broader concept of memory, the recollection of information. Memory is categorized in both broad and specific manners, and understanding each concept independently helps to truly comprehend the disparity between visual and auditory memory. Generally speaking, visual memory, as the name suggests, refers to the recollection of visual information, whereas auditory memories are the recollection of things that were heard.
Visual memories may be formed by the actual perception of a visual stimulus as well as from more imaginative sources. This encoding of stimuli occurs over time frames ranging from momentary, such as the blink of an eye, to longer term, such as the recollection of watching a movie. Of course, these memories may further be altered across time spanning months or years as well.
This particular subtype of memory is able to be stored due to the parietal and temporal lobes. These lobes are a part of the cerebral cortex, the outer layer of the brain involved in most "higher thinking" cognitive processes. The temporal lobe is located on the lateral aspect of the cortex and can be thought of as in the same region as the ear. The parietal lobe is above, superior in anatomical terms, to the temporal lobe, spanning the side and top of the cortex.
Due to the complexity of neurophysiological processes, the exact mechanism of storing visual and auditory memories is not easily articulated or understood. The same holds true for the storing of auditory, or echoic, memory. Echoic memory generally can only be retained for about three to four seconds, which is a relatively short amount of time. Other recollection of sounds, such as what a person was saying during a particular memorable event, is more attributable to episodic memory and other longer-term forms of auditory memory.
Therefore, visual and auditory memory differ specifically as smaller parts of a bigger mnemonic scheme. The difference is primarily the sense that is utilized to acquire the information in addition to the neural storage pathway. In visual memory, the eyes are used to sense reflected light, and the temporal and parietal lobes store the corresponding images. The auditory system is ear based and translates sound waves into particular vibrational patterns that are then interpreted in different ways by the brain to come up with specific sounds. If this sound is of any particular significance, it may then be stored as auditory memory in the brain and recalled for various reasons on both conscious and subconscious levels.