perception and components of memory

how does energy become a neural signal/representation

• transduction - transforming energy from the outside world into a neural signal (firing of neurons)

• sensation - picking up that raw signal from the outside world

• perception - recognising what that signal means eg. seeing a ball rather than a round blob

perception

however much information is out there in the world, how a particular person sees it depends on how the world is represented in their brain.

A stark example that is all in the brain: phantom limb

• illusions are important to understand perception

• because one way of understanding the brain is tricking it and understand why the tricks work

point of contact

the eye

top-down and bottom-up processing

Examples of top-down processing

• speech segmentation: speakers of a language can hear where one word ends and another begins even though the input is a continuous sound stream, knowledge creates the perception of individual words

• pain perception is influenced by placebo. Expectation that the pain will be reduced leads to refocussing of attention to other things, which in turn leads to pain reduction

visual perception is influenced by memory and context

theories of object perception

Helmholtz theory of unconscious influence: a particular pattern of activation in the retina can be caused by a range of objects eg.

• likelihood principle: we perceive the object that is most likely to have caused that pattern. This judgement is a result of unconscious assumptions (inferences) that we make about the environment and it happens ‘automatically’

• we see objects in a 3D world. If there is a chance to interpret an object as 3D we do. Illusion shows that we don’t see 2D objects as they are (equal in size). Instead we see the 3D shape of the objects in space.

the Gestlat Principles (grouping)

1. Law of Similarity - similar things are grouped together. You see rows of dots rather than just a dot pattern.

2. Law of Pragnanz - this law holds that objects in the environment are seen in a way that makes them appear as simple as possible. You’d see an image of overlapping circles rather than an assortment of curved, connected lines

3. Law of Proximity - things that are near each other seem to be grouped together

4. Law of Continuity - the law of continuity holds that points that are connected by straight or curving lines are seen in a way that follows the smoothest path. Rather than seeing separate lines and angles, lines are seen as belonging together

5. Law of Closure - according to the law of closure, things are grouped together if they seem to complete some entity. Our brains often ignore contradictory information and fill in gaps in information.

6. Law of Common Fate - states that humans perceive visual elements that move in the same speed and/or direction as parts of a single stimulus

using these laws we have now grouped bits in the environment into bits that belong together, bits that are an entity, an object. The next step is for the brain to figure out is what is that object, what characteristics make it a member of that category of objects.

monocular cues of depth

• perspective

• occlusion - where something is hidden or obscured from prominence or view

• shadow

monocular cues

• occlusion, relative size, relative height, texture gradient, familiar size, linear perspective, aerial perspective, shading, motion parralax

• arial perspective - because of the scattering of blue light in the atmosphere distant objects seem more blue (eg, mountains), on clear days the mountains seem closer; scattering of light also creates a blur, blurry things are further away, sharper contrast items seem closer

• light and shade - we have the light-from-above assumption, perspective changes when the image is viewed upside down

• monocular movement parallax - when the head moves close objects move fast, distant objects move relatively slowly

BUT we have 2 eyes

• binocular disparity - differences in the images of the two eyes

• stereopsis - disparity transformation into perception of depth

why 2 eyes

convergence

• overlapping visual fields enable stereoscopic visions by blending slightly dissimilar views of an object

• allows us to see farther into the distance with higher resolution

the interaction of perception and action

is movement necessary to develop normal vision? Held & Hein, 1963

• all active kittens developed a visually guided paw placement response after 63 sessions the latest (most had 33 sessions), none of the passive kittens had

• all active kittens avoided deep end of glass cliff, passive kittens went randomly to deep and shallow side

self produced movement and concurrent visual feedback are essential for the development of visually guided behaviour

From perceiving what to perceiving where

• data coming in from our eyes only means something when we can cross-reference it. We need feedback on what this information means. Hence, what we touch influences how we see.

cross cultural studies of perception

• provides evidence that the way we perceive the world depends on what surrounds us

• cultural influences due to factors eg environment, education, cultural history, language

Segall, Campbell and Herskovits (1963)

western cultures are more susceptible to the Muller-Lyer illusion and the Sander parralellogram illusion compared to cultures from rural Africa and the Phillipines

people who live in urban environment which contains more rectangular shapes are more prone to these (mistake lines as depth cues for distance)

people in rural areas experience more flat terrain and actual distance

Mayer & Rahmann (2018)

attentional blink paradigm where the second stimulus is difficult to process; Greek and Russian participants were better at discriminating the light from the dark blue stimulus (no difference for green) than German participants who performed the same for blue and green stimuli; light and dark blue have different names in Greek and Russian; native language influences our perception

colour vision

colour vision is affected by your native language. Other influencing factors are gender (many genes for colour vision are on the X chromosome making colour blindness more common in men); hormone levels also play a role and age (fades with age)

crossover in sensory modalities: synaesthesia

when presented with stimulation in one sensory modality, another modality is simultaneously activated; a blending of the senses occurs

components of memory

memory: process involved in retaining, retrieving and using information of the past which affects the present, possibly the future

the memory storage model eg Atkinson and Shiffrin (1968)

• sensory inputs persists very briefly, passively, in modality-specific temporary buffers (‘iconic’ memory for vision, ‘echoic’ memory for audition, etc)

• only attended items are identified and represented in a short term store (STS), where they can be operated upon, used to initiate/guide action or transferred (by rehearsal) into long term storage (control processes required)

• STS capacity is very limited: contents decay or are overwritten/displaced by new input or by information retrieved from long-term storage unless deliberately maintained by rehearsal

short term/working memory - Baddeley and Hitch, 1974

components of long term memory

three reasons (a priori) for posting that working memory and long-term memory are separate

• introspection: ‘primary’ vs ‘secondary’ memory (James, 1890)

• physiology:

  • info stored in current neural activity vs changes in synaptic strength

  • something most hold new information during initial ‘consolidation’ into longer term memory (requires protein synthesis)

  • reverberating circuits? (Hebb’s 1949 ‘cell assemblies’

  • cells in monkey prefrontal cortex show sustained activation in delayed-response and delayed match-to-sample tests

• complex information processing systems (eg computers) use temporary ‘work spaces’

  • to keep information being operated on readily available

  • to temporarily store information that is not worth storing permanently

working memory aka primary memory, short term storage (STS), ‘active’ memory

• arguments that working memory is distinct from long term memory come from

  • introspection

  • physiology

  • consideration of computational utility

  • experiments on normal subjects

  • effects of brain damage

to test whether our minds do have this type of temporal storage we need tasks that measure memory for very recent information

measuring short-term forgetting

The ‘brown-peterson’ distraction paradigm

• participant reads a short list (of 3 words/letters in this example), tries to retain it while eg counting backwards by threes, until cued to recall

• retention interval varies from trial to trial

• retention rapidly declines over time, then levels off: two memory components?

Free recall

• S sees/hears a long sequence of items

• at the end of the list tries to recall as many as possible in any order. If one asks to recall the last items first, they are relatively well remembered (recency effect)

explaining the pattern of short term forgetting

• single trace theory: memory trace decays rapidly to start with, then more slowly

• dual trace theory: retrieval after short interval mediated by temporary rapidly-decaying memory trace; retrieval after longer interval mediated by a more permanent memory trace

• the dual trace theory would be supported by:

  • retention over a short interval influenced by factors that don’t influence retention over a long interval (factor A)

  • retention over a long interval influenced by factors that don’t influence retention over a short interval (factor B)

  • ‘double dissociation’ between the effects of factors A and B

factors selectively impacting free recall

list length: the longer the list the fewer items are recalled BUT recency effect is unchanged

Glanzer & Cunitz (1966)

faster presentation rate reduces recall of items presented earlier

but not of the recent items

Same for: longer list, old age, alcohol

so far, a single dissociation : consistent with a single memory trace whose decay rate is changed by these manipulations. Double dissociation needed (ie a manipulation that zaps recall of recent, not earlier, items)

counting backwards after the end of the list eliminates the recency effect, but does not influence the probability of recall of early items

• double dissociation

  • so, recall of last few items mediated by a memory trace rapidly lost in the absence of rehearsal

  • earlier items recovered (if it all) from a different, more permanent trace

recap: components of memory part 1

double dissociations between short term and long term memory (disturbing the recency effect - STM, disturbing effects on items presented earlier - LTM)

visuo-spatial memory

how do we know there are distinct memory stores?

vision

→ iconic sensory memory

→ visual short-term memory

→ visual long term memory

Partial report of brief displays (Sperling, 1960)

• briefly flash 12 letters, 3 rows - have to write down as many as you can

• 4 correct is typical

• people say that they can briefly see all the letters as visual objects: they just don’t have time to identify more than about 4, before the image is gone. So, it seems visual sensory memory can hold about 4 items.

• same thing repeated, but row is specified

• people tend to get 3 or 4 right. As researcher could have cued you to look at any row, and there are 3 rows, we can estimate from the accuracy of your partial report that something like 10-12 items were (in principle) available

Sperling’s ‘partial report’ superiority effect

• report of whole array poor (3-4 items)

• cued report of single row good (3-4 items)

• why the difference? for the whole report it takes time to say all the letters and after about ~1sec the sensory memory is lost

• reporting the single row is quick, but the ‘partial report superiority’ is also lost when the cue comes after 1 sec, same reason, sensory memory trace has faded

change detection experiments with non-linguistic spatial arrays (Phillips, 1974)

visual working memory and change detection

• brief interpolated blank frame produces transients all over the visual field: attention no longer automatically attracted to region of change

• now the only way to detect a change is to compare the present display with memory for the objects in the previous frame

• under these conditions we don’t easily detect changes - unless we happen to have just attended the region of the change

  → very limited memory for the objects in the previous frame: ‘change blindness’ (Resinck, O’regan & Clark, 1977)

change blindness and the transition from iconic to visual working memory (VSTS)

• different attributes (shape, colour etc) of objects presently in the visual field are represented by local activity in several visual cortex ‘maps’: separate maps for features such as orientation, movement, colour

• this sensory activity persists beyond the stimulus offset (sensory memory) unless overwritten by a new retinal image, but not for long

• while it remains available, binding features by focal attention creates ‘object files’ in visual working memory (or VSTS)

• unless you have attended to an object in the previous frame and its file is made it into visual working memory (VSTS), you won’t detect the change

how many objects can VSTM hold?

• vary number of objects in ‘one-shot’ change detection task

• only about 3 or 4!

is visual STM distinct from long term visual memory?

sequence of 8 Phillips checkerboards, followed by a sequence of test checkerboards same as/different to each pattern in the first sequence, but in reverse order

• ‘recency effect’ - final item much better remembered

• recency effect was eliminated by 5 secs of mental arithmetic

slower presentation rate improved memory for all but the last item

• double dissociation

so, the most recent complex array seen is held in visual STS

previous patterns recovered (if it all) from distinct long-term visual memory

summary: memory so far

• behavioural evidence that there are distinct stores for working memory and long-term memory

• is this true for all sensory information?

• we looked at the case of vision: distinctions between iconic sensory memory, visual short term memory and visual long term memory