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1

the visual search exp

Can we process info from whole visual field at once? Or must we process one object (/region) at a time?

Depends on what kind of processing required?

Treisman and Gelade (1980) measured time taken to search for target object differing from background objects, and varied number of objects N in display:
- If process one object at a time, then larger N is, longer should take to detect prescence/absence of target
- If can perf necessary discrimination for all objects on display simultaneously, time taken to detect presence absence target shouldn’t increase much with N

Target differed from background items by:
- Single feature
- combination (/conjunction) of features

On each trial, see array of ‘objects’ - blue, green/brown, Ns, Xs/Os

2

the Stroop effect

First reported by Stroop (1935)

Much harder to name colour of names of colour than other symbols

Exp on:
- Selective attention - asking subject to selectively attend to one of two attributes of object and ignore other
- Control of cog processes - have 2 familiar stimulus-to-action mappings in comp - greater RT for naming coloured cowards than control items (interference/response conflict effect) measures difficulty of suppressing more practiced but irrelevant reading response
- Effects of emotion on attention and control because in some lists we use emotion words

3

control of task-set

Each stimulus in current env affords many tasks

Can select ‘at will’
- Which stimulus/attribute to process - Attentional control
- Which cog task to perf- Intentional control
- According to current goals
- Appropriate organisation of processes to carry out particular task = ‘task-set

4

the task switching exp

The processes that reorganise the mind to do one task rather than another = ‘executive/control’ processes

5

visual search

Anne Treisman (PhD Oxford, 1960)

6

exp design IVs

no. of items on display - no. varies unpredictably from trial to trial, objects positioned randomly in grid

Target present on half trials, absent on others - varies unpredictably from trial to trial

Target differs from background by either
- Single feature
- A feature conjunction

Manipulated between blocks of trials, order balanced

7

exp design DVs

RT

Error rate

8

prediction: illusory conjunctions

Very brief display (200ms) followed by pattern mask: P told to attend to and report lateral digits - then cued to report object in one of 4 (unattended) locations by features: e.g. ‘big outline red circle

More reports of erroneous conjunctions of features from display: e.g. outline green circle’ than would be predicted by random guessing from the set of colours, shapes etc. used in the exp

Need attention to bind features together

Patients who have difficulty finding conjunction targets (cannot find Wally) and are esp. susceptible to illusory conjunctions (Balint’s syndrome) and can search for only one feature

9

visual attention in complex scenes

Details of Treisman’s account of visual search have been challenged
- For many target/distractor pairs, pref in between ‘serial search’ patterns dn ‘pop-out’ pattern
- Slow of search function depends on target-distractor similarity (not just conjunction v single-feature)

however, amendments to theory leave idea intact that features of not-yet-attended objects not ‘bound’ into object description

Adds to other demonstrations that processing unattended visual objects shallow

10

response neg v neutral words in depression

Mitterschifthaler et al. (2008)

Main effect of valence (sad > neutral), group (MDD > controls), valence x group (MDD > controls for negative, not neutral words).

L ACC activation (negative > neutral) was greater in MDD than controls. ACC activation correlated positively with latencies to negative emotional words in MDD (r = 0.68, p = 0.003). Rostral ACC involved in attention allocation and conflict monitoring

Slowing of 100ms (84ms on average across clinical studies)

11

response to neg v neutral words in healthy controls

Emotional stroop shows slowing to disorder-relevant words (threat words in anx, injury-related in PTSD, food in bulimia, exam/achievement in students before exams etc)

Both ‘relatedness to current concern’ and negativity cause greater interference in patients

Unclear what it really measures - selective attention, interference from emotional reaction, ‘cog avoidance’ (suppressing the meaning of word), mental preoccupation?

Effects seen with subliminal presentation

12

emotional stroop

Colour name neg, pos, neutral words

Time taken to name colour increases as attention to emotion word increases

Patients with depression tend to be slower to name the colour of neg words (indirect neg bias)

Used as an indirect measure of emotional bias in psych disorders (as opposed to e.g. recognising emotions in faces, which is a direct measurement of bias)