Cognitive Psychology Part 1

Cognitive psychology studies human behaviour from an 'information processing' point of view.

It focuses on the processes that take place in order for a given input to result in some output.

It views the brain as an info processing machine, much like a computer. 

Not all cognitive processes result in overt behaviour. We can imagine things without being exposed to an external stimulus.- both of these are difficult to study.

Attention, perception, memory, ----> higher level processes: problem solving, reading, decision making, reasoning

Bottom up processing refers to processing sensory info as it comes in.- purely visual

E.g. image is shown to you, your eyes detect the features, your brain pieces it together and then you percieve it as an eagle.

Top down processing refers to perception that is driven by cognition- your brain applies what it knows and what it expects to percieve and fills in the blanks.

There is a long term memory storage where the memory strength of an item decays over time. Rehearsal helps to overcome decay.

The short-term memory buffer stores only the most recently presented items and keeps them active for immediate use.

Atkinson and Shiffrin (1968)- Observed data to support the theory.

How do we acquire info from the environment- The visual system

How do we select and process relevant info oout of the overwhelming amount of stimuli surrounding us? Attention

Theory of attention: early vs late selection

Theoies of visual attention- Navon

Newton (1704)- light as a stream of particles (photons)

Maxwell (1873)- light not only travels as a straight line, but as an oscillating wave. It has a wave length.

Visible light - 380-760 nanometers

Light enters the eye via the pupil (a hole in the iris), to the lens

The lens focuses the light on the rear of the eye- the retina- where electomagnetic radiation is transformed into neural signals.

Two types of visual receptor cells in the retian- rods and cones

Rods: Dim light and movement. About 125 milion in periphery

Cones: Colour and sharp vision. About 6 million, mostly in fovea.

Nocturnal animals such as Owls have only rods

Diurnal animals such as Pigeons have retinas that are all cones

From the retina, the visual pathway goes via the optic nerve to the optic chiasm and the to the primary and secondary visual cortex (V1 and V2 respectively).

V1 is organised as a retinotopic map: its nerve cells spatially correspond to the receptive fields on the surface of the retina.

There are two pathways from the retina

1) Colour and fine details (what)- Ventral

2) Movement (where)- Dorsal

We have limited resources for processing and responding to stimulus.

With very sensitive sensory systems but with limited processing resources, a conflict ensues. Therefore, we need attention- selectivity of processing

Theories of attention

1) Broadments filter theory- Dichotic listening task- little info extracted from unattended ear. Concluded only one of two inputs is allowed access into a limited capactiy processing mechanism. Selection is based on the physical characteristics of the input and only the selected input is thoroughly processed for meaning.

2) Triesmans attentuation theory- filter reduces/attenuates analysis of unattended info. Thresholds for relevant stimuli are lowered, threshold for name would be fairly low so it could be detected if presented to the unattended channel

3) Deutch and Deutsch theory- Late selection- all stimuli are analysed but only the most important or relevant stimulis determines the response

4) Lavie: perceptual load theory- selection is sometimes early and sometimes late- limited attentional capacity. The amount of attentional capactity allocated to the main task depends on its perceptual load. Total available capacity is always allocated to processing. Any spare capacity is allocated to irrelevant stimuli.

What is selected by the selective/focused visual attention mechanisms?

-location-based attention

-object-based attention

Attentional spotlight- Posner (1980) suggested a covert attention mechanism that shifts to different spatial locations in the absence of eye movement.

Le Berge (1983)- presented 5 letter words, followed by * that could appear in location of any of the 5 letters and required a rapid response.

In one condition the participants' attention was directed to the middle letter by asking them to categorise the letter (vowel/consonant)

In another condition they were require to categorise the whole work (broaden their attentional beam).

Faster respones in word tast than letter task

Challenges to this location-based visual attention: ambiguous figures-  attention can be allocated to one of two figures that occupy the same spacial location

Evidence for object-based visual attention- O'Craven, Downing & Kanwisher (1999)- presented 2 stimuli transparently overlapping at same location, with on objet moving slightly. Participants were asked to attent to the direction of motion of the moving stimulis or to the location of the stationary stimulus. If attention is location based, participants should attend to both stimuli since both the house and face occupy the same location. Using fMRI, they found more activity in the 'face area' (FFA) when the face stimulis was attended than unattended, and more in the object area (PPA) when the house was attented than unattended

It can be location-based or object-based

It is often object based, given that the goal of perception is generally to identify objects in the environment.

It is still unknown whether they can occur at the same time but Mozer & Sitton (1998) argue object-based selection operated either before or at the same time as location-based selection.

Faces are so special they deserve their own brain area.

Face-specific activation happens in parts of the right fusiform gyrus (FFA)

It has been claimed that we have developed expertise in recognising faces.

E.g. Feature integration theory

Search for one featrure (e.g.colour) unaffected by set size as it pops out

Search for two features (e.g.colour+form) affected by set size.

Treisman- rapid initial parallel process, where features of objects are processed.

A slower, serial process in which features are combined to form objects

Features can be combined if attention is focused on the location of the object- attention is the glue that binds features into objects.

If we search a large set for a conjuctive target (colour+form, blue x) it takes time for the serial search- accompanied by shifts of focused attention to detect a target. The outcome is RT increase with set size.

Illusory conjunctions- in absence of attention- improperly combine features into objcts