Global v Local processing Flashcards
What stages are thought to make up the process of perception?
An initial passive perceptual stage during which our senses receive info from the environment and suggest possible interpretations based on that
A secondary active stage during which the most promising interpretation is followed up by interrogation of the proximal stimulus to check sensibility of the suggestion
What would Gestalt suggest?
Perception occurs in a global-to-local fashion wherein the object is perceived as its whole, which is different from the sum of its parts GLOBAL PRECEDENCE (forest before the trees)
What were 3 findings from Navon’s compound letter stimuli experiments?
1) Global preference - global level faster regardless of congruence
2) Global-to-local inference - global aspect slows local processing in incongruent tasks
3) No local-to-global inference - incongruent local letters did not slow response times to global
What are 2 simple ways to explain Navon’s results?
Internal letter detectors operating one after another - the global detector sets off first and the local second. Decision stage of processing has to wait for the local detector to finish the race before any decisions can be made as to local identity Parallel processing (horse race) - race starts at the same time but "rise-time" is shorter for the global horse so it wins the race
What did Navon suggest about the global precedence effect?
May be modulated by display/demand characteristics so maybe more appropriate to consider it simply indicative of a general perceptual disposition to favour a whole over parts (selection of cluster properties form a particular recognisable pattern)
What is meant by Global Addressability?
How contact occurs between an incoming stimulus and object schema in the memory store - e.g. “ripe old age” painting, global constituents of face schema invoked by the overall pattern of stimuli rather than analysis of the “facial” features which would match schemata for fruit and veg
What 4 factors have been argued to influence the global precedence effect?
Sparsity of local elements
Visual angle and size of stimuli
Retinal position (where letters positioned relative to fixation)
Exposure duration (masking)
What did Mevorach et al find in their experiments on global precedence?
Changed the size of the compound images and found that when the compound letter is smaller the global precedence effect is strongest (greater interference in identifying local)
However, when compound letter was larger, there was local precedence and the congruency effect was larger in the global condition i.e. more interference
What is meant by universalism and how does this apply to global precedence?
Idea that everyone has the same cognitive processing, performed in identical ways
Research into remote tribal cultures suggested this was incorrect e.g. tribes not fooled by illusions
Davidoff et al found that the Himba tribe showed local preference while British showed global - urbanised Himba showed global too
What did Davidoff et al’s experiments with the Himba suggest?
Something about urban environments promotes global processing - perhaps survival advantage in crowded scenes
So the sequence of processing must be malleable and adaptable to new environments (rural to urbanised)
What is meant by hemispheric lateralisation and what suggested this for global-to-local processing mechanisms?
Extent a cognitive process is specialised in one particular hemisphere
Separate mechanisms because different reaction times and able to be manipulated in different ways
What did Delis et al suggest in their experiments?
Global processing lateralised to the right hemisphere and local lateralised to the left
Used lesion patients (but don’t know what they were like when healthy so results don’t provide guaranteed cause-effect)
What did Yovel et al find in their lateralised presentation studies using neurotypical individuals?
When compound letters presented to left and right visual fields, there was a benefit for global targets when stimulus presented to the left visual field (i.e. right hemisphere) and a benefit for local targets when presented to right visual field
What evidence has contrasted with Yovel et al’s and others’ findings?
Fink et al found evidence of local-to-global precedence when using different non-letter stimuli, and other studies have suggested bilateral specialisation/no hemispheric lateralisation at all
What is simultanagnosia and how did Huberle and Karnath, and Shalev et al provide evidence for this?
Inability to process multiple items in different levels at once, only one at a time e.g. only see local or only see global - multiple items at local level captures attention more than global
They changed distance between local elements and made them bigger, and found that patients with bilateral parietal lesions could perform both global and local processing in these conditions
Studied Balint syndrome (bilateral lesions) and found deficit in global processing primarily when local distractor items unfamiliar
Thus no certain evidence of lateralisation - sometimes patients with deficits can perform when conditions manipulated
