Perception and Memory

Perception and memory can be defined as constructive and re-constructive processes. When we experience the world we assume that we are perceiving it in real time (smoothly) as it currently exists, but that’s not true. The brain refers to a set of heuristics and short cuts based on the physics and statistics of the natural world to process sensory information, then fills in the gaps based on past experiences to create the most plausible reality based on the content. Short term memories can warp our perception, frame our long term memories, and trigger old complex memories with a simple a scent.


The Chauvet cave paintings, France circa 30,000 BP: show how imagery retained in the mind’s eye influences visual perception – the painting of the top rhinoceros may represent a memory of motion.

To better understand the role that memory plays in the processing of perception, lets first look at the types of memory.

Sensory Memory: Sensory memory is short term memory (a kind of buffer) that records information before it is processed. Each of our senses has its own storage of short-term memory (in differing capacities) and we do not perceive or experience this information.

Working memory: Working memory is a secondary short term memory that acts as a kind of scratch pad where information is stored for current focus of conscious attention. Working memory is needed as mental tasks are carried out for processing perception and short term mental functions. Working memory can hold between 5 to 9 items and depending on the type, holds information from a few milliseconds to up to 10 seconds (just try to remember the past few text messages you sent). Working memory can contain errors depending on how taxed the senses are (optical illusions are sometimes an example of over taxing). Perceptions in working memory are either moved on to long term memory or lost. Keeping notes is a common method for offloading working memory before it is lost.

Long Term memory: the long-term storage for the brain, which can affect perception performance base on familiarity with systems, like graphical elements, are important Graphical elements are remembered better than text-based command-line user interfaces. Memories will be moved to long term if they “stand out” vs. those that are repetitive or effectively in the background. Long term memory may seem solid and safe, but can be suppressed and/or inhibited, falsely implanted, implied, and/or distorted.

Perception Memory Characteristics
Some examples of memory that effect perception.

Motion after effects: occur after looking at a moving stimulus for several seconds and then shifting your gaze to a stationary one, which then appears to move in the opposite direction to the first.

After Image Effect: visual illusion in which retinal impressions persist after the removal of a stimulus, believed to be caused by the continued activation of the visual system.

Load Induced Blindness: Our senses can be overwhelmed by information – think of a visually busy room, crowded with people talking and loud music – it can make stimuli difficult to see and remember (for example, the Invisible Gorilla Experiment). This is why crisis communication experts say that a message should have no more than three main points– it’s because it’s difficult for people to retain more in their minds.

Change Blindness: We believe we perceive everything in the world around us but our brains are very selective. Change blindness is a perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it. The door experiment is an eye-opening example:

Boundary Extension: a phenomenon of false memory. Boundary extension is when we tend to remember a scene (image or location) as though more was visible than what we actually saw. Boundary extension is usually interpreted as a constructive memory error—our memory system extrapolates the view of the scene to a wider angle than was actually present.

Spatial updating and Trans-saccadic perception: Spatial updating occurs when you see an object just before a saccade, and allows you to “make another saccade back to that image, even if it is no longer visible.” The brain somehow “takes into account the intervening eye movement by temporarily recording a copy of the command for the eye movement” and compares it to the remembered target image. See Saccadic eye movements

False memory: This perception issue seems to occur over a period of time (within 42 milliseconds vs an illusion which is almost instantaneous). False memories are often seen in mistaken identity. One example involved a cognitive psychologist who was arrested, made to pose in a witness line-up, and identified as the perpetrator of a rape. Luckily the psychologist had an alibi – he was appearing on a TV program discussing methods for improving facial memory.

Web Applications
Understanding how memory affects and augments perception is essential for good Web development. Here’ are some points every Web developer and communication expert needs to know.

  • Reduce working memory load: try to minimize situations where the user must remember temporary information.
  • Use Graphic Interfaces: graphical icons are easier to recognize and remember than text. They require far less mental effort (saving working memory for the user) than text.
  • Keep commands and actions consistent: User interfaces where commands work in a consistent reduce memory demands on the user.
  • Use Web conventions: for example, change the color of visited links so that users don’t have to remember where they’ve already clicked.
  • Remember for a user when possible: example, if you offer a coupon code (say in an email), don’t make the user remember that code, send it to the store checkout area to wait there for them.

HCI research video

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