Modelado del intercambiador de calor

As outlined above, previous paradigms may have masked the magnitude o f the popout effect due to the intrinsic similarity of the stimuli used. One way to minimize such similarity is to define each o f the objects in an array by a unique perceptual dim ension. In the present study, this was attem pted by defining each o f the array objects by a unique colour. The justification for using colour was based on the fact that there are three distinct receptor types on the retina which combine to give four distinct perceptual dim ensions, ie. Blue, Red, Green and Y ellow . Therefore, if each of the four array objects was defined by each o f the four colours it was thought that similarity among the array objects w ould be minimized.

H ow ever, in order to replicate the novel popout effect, a minimum o f five distinct dimensions are needed. A dimension is needed for each of the four fam iliar objects in an array and an extra dimension is needed for the novel object introduced to an array. One simple solution to this problem w ould be to investigate popout with arrays o f three objects rather than four. H owever, this solution was rejected as it would alter the configurai aspect o f the arrays which may make com parison with the previous studies m ore difficult. To retain the configuration o f four objects, the set o f colours defining array objects was extended to five by introducing the colour Cyan (Blue/Green). But by assigning Red as the colour o f the novel object it was ensured that there was no dim ensional overlap with the colours o f the fam iliar objects (ie. Blue, Green, Yellow, Cyan).

The prediction that attention to the repeated stimuli is unnecessary was addressed by maintaining the irrelevance o f the colours throughout the task. This was an attem pt to return to the functional questions addressed in Chapter 4. H ere it was argued that novel popout is induced by a mechanism which functions to filter out "irrelevant stimuli". B ut in previous studies the stimuli used have been both irrelevant and relevant at different points in time. Consequently, there is no conclusive evidence that irrelevant stimuli can induce popout.

To maintain the irrelevance of stimuli throughout the task a variation on the cue-target paradigm was devised. As in previous popout studies the target stimuli are words that subjects must locate at one o f four positions in the display. However, unlike previous studies, the four positions are now pre-cued by non-target colour stimuli in the display. The colour stimuli w ere four square blocks on which the target words w ere written. The cuing effect was achieved by expanding the spatial resolution o f the display to give the impression o f four blocks approaching from a distance. At a low spatial resolution objects appeared "far away" so th a t the w ord stimuli could not be identified but the colour o f the square blocks could. However, as the spatial resolution increased and the objects "approached", the subjects were able to identify the target words. Thus, the coloured blocks served as m ultiple sim ultaneous cues o f the target w ord locations. By manipulating the familiarity o f these blocks it was

intended to bias selection to favour one block location above the others.^

In all, four conditions o f bias were examined. In the One N ovel condition three colour cues are familiar but one is novel. According to the revised GAIN model the familiar cues should activate an N -node representation which reduces their probability of selection. As a conseq uence, a bias is expected to the lone novel cue. In the All Familiar and All Novel conditions, all colour cues have equivalent preexposure history, (or equal valence^), therefore no selection bias is expected. Finally, in the One Familiar condition a lone familiar cue is p resen te d w ith three novel cues. In this case the lone familiar cue will be insufficient to activate an N -node representation and again no selection bias is expected.

7.2.1 Method

Subjects.

40 undergraduate and graduate students (Age: 18-32yrs). 26 Ss were fem ale and 14 male. All w ere naïve as to the purpose of the experiment.

A pparatus and Stimuli.

The displays presented to subjects comprised of a series of short anim ated clips. Each animation depicted four square blocks, all identical in size. The blocks could vary in colour

As a real life analogy to the task consider walking down a high street in search o f a M idland bank. Each o f the buildings in the street has its own sign, identifiable by words and colours. But, at a distance the words on the signs wiU be unreadable. In this case search may be guided by a simple visual feature such as the colours blue and yellow which characterise the M idland bank sign. In other w ords, a selection bias is introduced through colours which have associated with a particular goal. In the present study, an attem pt is m ade to induce a sim ilar bias by manipulating the familiarity of colours. H owever, in this case, the colours them selves have never been associated with the goal.

2

New English Dictionary: VALENCY

The pow er or capacity o f certain elements to

combine with or displace

other elem ents. " I think it will probably be found that the atoms o f high valency are really molecules." (1881). " T he m olecule is a body in which all the attractions or valencies are satisfied, leaving the com bined atoms to act as a w hole from one centre." (1869).

and upon each was either a five letter w ord or a non-word. In total eleven anim ations were constructed. Four w ere assigned to orienting trials and seven to the PX trials. The orienting trial animations had tw o words and tw o non-words superim posed on the blocks (See F ig.7.1). The PX trial animations had four non-words superim posed on the blocks (See Fig.7.2). A detailed description o f the block colours is presented in the following section. All animations were constructed on a 3-D m odelling package (3-D studio) and presented w ith a m ulti-m edia animation player (Soundscript).

T o create the animation, blocks w ere viewed from a "camera" position that m oved along an axis perpendicular to their faces and passing through the centre o f the configuration. W hen presented as an animation, the cam era motion creates an impression o f four blocks loom ing from a distance tow ards the subject. Rendered frames to illustrate this effect are presented in Fig.7.3. Each anim ation com posed of 30 frames and was presented at a rate of 20 fram es/sec. Thus, a com plete animated clip had a duration o f 1.5 seconds. The visual angles subtended by the whole configuration o f blocks varied from a 5.0 deg to 20.2 deg, horizontally and vertically.

D esign and Procedure.

The forty subjects w here randomly assigned to one o f four conditions. One Novel, All Familiar, One Familiar and All Novel. Subjects in all conditions w ere presented with a

continuous

sequence o f twenty-four animations. The sequence com posed o f a repeating cycle o f five PX trials (PX-T) followed by a single Orienting trial (OR-T). The four Orienting trials were

identical across conditions.

As shown in Fig. 7.4, they w ere constructed from a single tem plate by replacing each o f the four colours with the colour RED. The subject's task th ro u g h o u t was to look for w ords in the display. W hen they detected a w ord they w ere to name it out loud. D uring PX trials no words could be detected as only random letter strings were present on the blocks. However, on Orienting trials the blocks contained two w ords and two random strings. The crucial measure was which of the two words in an O rienting trial the subject selected first. To bias this selection process the four conditions manipulated the relationship between block

colours

in PX and Orienting trials.

MNOCP

7.2.2 Colour Manipulation

The diagram in Fig.7.5 illustrates the manipulations for One Novel and All Familiar conditions. Letters on the blocks indicate their colour. The shading of blocks indicates whether they contain words or non-words. In the One Novel condition a bias is introduced by changing the block colours between PX and Orienting trials. Thus, on each Orienting trial one of the word blocks stays the same colour as on the previous PX trials whereas the other block is changed to the novel colour RED. By contrast, in the All Familiar condition the block colours remain consistent as the displays progress from PX to Orienting trials. Therefore, in this condition, there is no bias in the relative familiarity of block colours. The diagram in Fig.7.6 illustrates the manipulations for One Familiar and All Novel conditions. Again letters on the blocks indicate their colour, and shading of blocks denotes the presence o f w ords. In the One Familiar condition a bias is introduced by keeping the colour Red consistent from PX to Orienting trials. Thus, on Orienting trials, the Red word block is a familiar colour whereas the other is a novel colour. By comparison, there is no colour bias for word blocks in the All Novel condition as all colours are novel on Orienting trials.

PX-T

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