One of the original models of memory was the modal model introduced by James in 1890 (Healy & McNamara, 1996).  This guiding framework for research in the area of memory distinguished between primary and secondary memory.  James described primary memory as that which is held only for a moment in our conscious mind and secondary memory was held in our unconscious and was considered permanent (Healy & McNamara, 1996).  From the time when this original model predominated, many researchers have been involved in the investigation of our memory processes.  Atkinson & Shiffrin (1968) added another element to the memory dichotomy – sensory memory.  The sensory memory was thought to have separate registers for different senses, including visual, auditory, and haptic.  Also included in their theory of memory were various control processes; most popular was the rote rehearsal process.  This process was described in terms of a rehearsal buffer in the short-term memory storage.  Each stimulus item referred to a fixed-capacity rehearsal buffer and displaced a randomly selected item already there when the capacity was full.  As long as the item was in the buffer, information about it was transferred to the long-term memory.  The amount of information transferred was a linear function of the time in the buffer.  When information was needed, information items from the buffer were initially extracted, and then further searches were made of the long-term memory storage if more information was required.

An important element of this modal model was that it assumed that an item could be retained in the short-term buffer as well as in the long-term buffer at the same time.  Further to this, the recall of any particular item, including the most recent ones, could be retrieved from the short-term storage and the long-term storage.  Of great interest to researchers of memory were the effects of such variables with the presence of a distracter task, the rate of item presentation and the list length of items.  According to the modal model, there was an advantage in which order the items were presented.  Items were stored linearly in the buffer.  The most recent items were stored at the top of the buffer, and the more mature items were stored at the bottom or the centre of the buffer.  The recency effect implied that the most recently presented items were at the top of the buffer and could be easily accessed for quick recall.  There was also an advantage of the items presented to an individual first because these items stayed in the buffer longer than the items following them, so more information could be transferred to the long term memory storage.  This was called the primacy effect (Healy & McNamara, 1996).

In more recent research on memory, Anooshian (1998) suggested that there was a contrast between memory successes and memory failures that appeared to reflect the distinction between implicit and explicit memory.  She provided an example of how she and her daughter strolled down the rows in a grocery store containing flour, sugar and other baking goods.  Her three-year-old daughter told her that these things (ingredients) could be put together to make cookies.  Anooshian was surprised by her daughter’s comment because she couldn’t remember ever baking cookies at home.  When she questioned her daughter about how she knew this bit of information, her daughter responded, “I don’t know why I thought of it… it just ‘popped into my head’ while we were walking…sometimes things just pop into my head like that.”  Then later, her daughter revealed where the information had originated in another comment, “You know mom, Mr. Rogers makes cookies that way.”  Then Anooshian realized they had watched Mr. Rogers bake cookies on his television show a few days prior shopping at the grocery store.  This, Anooshian suggested, demonstrated how there were many levels of memory processes working simultaneously.  Anooshian’s  (1998) research concentrated on the unconscious influences of memory on different memory retrieval processes, including implicit and explicit processes, when individuals are generally aware and conscious of their surroundings and task demands.

From one perspective, if looking at the negative colors of the image, two faces appear to be staring at each other.  However, when looking at the image through the positive perspective, there appears to be a large white vase with a large foot base, on the center of the page.  This is an optical illusion that can be seen from the negative perspective, the positive perspective, or from both perspectives.  Rarely do people see both perspectives simultaneously.  Sometimes, in fact, individuals are told about the existence of the alternate image, but can still see only one image (negative or positive, whichever perspective they view the image from).   Framing effects are also visual illusions (Tversky & Kahneman, 1986).  An option can be phrased positively or negatively, and the outcome can change due to the phrasing of the option rather than true differences that exist.

Another type of obstruction is memory illusion.   This is simply that the sensory data is no longer available.  Based on our memories we make judgments that may be in error.  Memory errors are even more difficult to become aware of because we often cannot compare our memory to the actual event.  This is a similar interpretation to Gingrich and Soli's (1984) interpretation of how the working memory can be put under higher levels of demands when the information presented to the respondent is either inadequate or in error and does not make sense to the respondent because they are missing the comparable information in their own memory.  Fuzzy-trace theory can also be used to explain memory phenomena in a variety of tasks.