2135 A Sep 16 - Lecture Notes PDF

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Lecture by Steven Lupker on the topic of sensory memory and how it came to be ...

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Sensory Memory Saccade - rapid movement of the eye between fixation points. ● Our eyes don’t move around smoothly, they jump from place to place. ● You will be stationary for a millisecond and then jump in about 50 milliseconds, during that time, you can’t take any information. ● 200 milliseconds of seeing and then 50 milliseconds of not seeing but the world still looks continuous. ● Therefore, the concept of sensory memory comes in because there is some system that allows us to perceive, even when there is a break in our vision. ● In the 1950s, people believed that our visual system was continuous and there was no need to consider the possibility of sensory memory.  George Sperling ○ He was interested in how many things you can perceive in one glance ■ What is the span of apprehension ○ Short term memory had started being studied with passion during this time ○ Showed people various arrays of letters, on a screen. Anywhere from one to 12 letters, varying from letter to letter. Task: Report as many letters as you can. Letters were only there for 50 milliseconds ○ He found if you 1-5 letters, people would usually be able to recall them all ■ Referred to as the whole report technique ■ Normal dependent variable: probability correct ■ Sterling’s dependent variable: number of items available to report ■ So he found around 4.5 to 5 items are available to report ■ Limitations: ● You may have seen more than the letters you report but short term memory limits your capacity so chances to recall all the items you saw are low ● Interference - you  get the sequence of numbers but while you are trying to remember the first couple numbers, you forget the rest because the information starts interfering ○ Sterling created the partial  report procedure to combat the first limitation ■ You are presented with a stimulus for 50 ms and then at some interstimulus interval after the stimulus has gone away, you get an auditory queue that tells you which part of the sequence you are supposed to report ■ He found that you can get pretty close to being perfect if the queue was given very quickly. Brighter stimulus = performance goes up, blurry and dim = performance goes down. ■ If you have a queue early enough, everything will go into short term memory ○ Interstimulus interval (ISI) - when one stimulus ends and when the other one begins. ● If everything gets in short term memory, then it is not visual anymore. So, the visual nature of the queue should not matter.  Stimulus is NOT the same on every trial, it changes.

Averbach and Coriell (1961) ● Concluded that stimulus may be on screen for 50 ms but stimulus continues to be perceived after it leaves the screen, alluding to sensory memory system. ● They only asked people to recall one item out of the 16 displayed, in their experiment. ○ Eliminates issues with short term memory ● Used visual queues ● Performance goes down as intervals are delayed, better when they are quick ● They said if you are right and stuff is in STM, the nature of the queue should be irrelevant. When we use a bar marker, it is irrelevant. Visible nature of queue shouldn’t matter ● In the second condition, they used a circle with cross hatches inside (grid), occurring right on top where the letter used to be. ● If all this information is in STM, visual nature of the queue should not matter. ● Normally, short ISI, people recall better, if you let ISI grow, people recall worse. ● When the “grid” comes on top of the letter quickly, nobody recalled it. You can’t perceive the stimulus. Delaying the grid, gives you a better chance. You can’t see the letter because the stimulus has obscured it. ● The only way you can interfere with perception is if the perception is not over. If you can obscure it, even if the stimulus is gone, then it means perception isn’t over. Therefore, we have sensory memory, perceiving the stimulus even after it has been removed. ● They set off a tidal wave of backward masking experiments Backward masking  - interfering with something you did a while ago with something you’re doing now.  Present a stimulus then present another one shortly after, and the second one prevenits you perceiving the first one accurately. 

Sensory Memory → Short Term Memory Perceiving the features of a stimulus helps you recognize what it is. Over time, features accumulate and get tied together. Perception works as a feature cumulation process.  Pandemonium Model (1959) - based on the idea that we have a bunch of different demons that allow us to do things, they all have certain roles and do certain things. If stimulus out there is like what the demons are responsible, they start to show and the one that shouts the loudest, is the one that the letter is. Example: the letter R is seen by the image demon, then it goes into the cortical “stew.” then the feature demons, who each have a role in identifying (vertical line demon, horizontal line demon, right angle demon, etc). Feature demons record each line of the letter (vertical line demon recognizes the vertical line and so on). Then, the cognitive demons are responsible for each of the letters. Each letter has their own demon, and each demon gets excited when the feature demons find information that identifies with their letter. The R demon screams the loudest because it matches, then the decision demon evaluates all the information and the screaming and makes the decision.  1960: ● People tried to figure out what the features we accumulated were

● Scientists were interested in what mistakes we made when perceiving and how ○ If people confuse E and F, we can tell that they are perceptually similar and they share features. 1977: ● We have been working with the idea that perception is a feature accumulation process and we’re not getting anywhere. We don’t know what the features are or how they work ● Navon suggested initial moments of perceptions are something that later refine themselves -- what you get very early in perception is just a blurry representation of what the stimulus actually is. Like focusing ● Global to local processing - what you see initially is the global and what you see near the end is the local....