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Though the degree of ambiguity differs , every input to the brain can , and is , interpreted in more than one way by different individuals . These are the informed best guesses of each brain of what is out there that is meaningful to itself .
 
The fifteen randomly selected subjects under study were shown Figure 1 ( /exchange/ambigfig/gilbert ) . The overwhelming majority ( 13 out of 15 respondents or 87% ) identified the figure as that of a skull . When probed about what led to their answer , they typically identified the white expanse of the forehead , cheekbones and jaw . Only two respondents ( 13% ) said that the picture depicted two women , framed by a porthole / round window , sitting across each other at a formal dinner .
When exposed to Figure 2 ( /exchange/ambidfig/cheetahs )  , every respondent saw two leopards , one standing , and the other seated .
Working on the hypothesis that the sharp contrast in Figure 1 and the largely uniform tone of Figure 2 influenced the answers of the majority ,  respondents were shown Figure 3 ( /exchange/ambigfig/etching ) . The majority ( 87% )  responded with answers ranging from a grandfather to William Shakespeare though all indisputably related to a man . When asked what decided their answer , they again replied that it was the white expanse of the forehead and , in some cases , the upper lip . Only two ( seasoned test - takers obviously ! ) said that it  showed a meadow with  grand buildings in the background and a robed woman and the bole of a tree in the foreground .
Though each figure could have elicited more than one equally good spontaneous answer , there was one popular informed guess every time driven by the same reason . The brain evidently pays more attention to comparisons and contrasts than to absolutes . In a world driven by information overload and constant flux , the brain sifts through signals to decide which are worth its while to interpret . It allows large rivers of data to pass through almost entirely unassimilated , peeling off selected data for a close , careful  view ( Jeremy Wolfe , Harvard Medical School ) . Picking the " out of the ordinary " or the different , the high contrast , is perhaps one way in which the brain decides what to focus on .
 
According to Natalie Angier ( The New York Times , April 2008 ) , the mechanisms that succeed in seizing our attention fall into two basic classes : bottom up and bottom down . Bottom-up attentiveness originates with the stimulus , with something in our sensory field that is the equivalent of a sensory shout - the expanses of white standing out of the dark background in the examples discussed earlier . In comparison , top-down attentiveness is volitional - the decision by the subject that an item , even in the absence of sensory shouts , nonetheless merits attention .
Respondents were shown two photographs of themselves as part of a group , taken in quick succession and with barely perceptible differences . With the photographs removed from view , they were asked if the two photographs were different in any way . Only three ( 20% ) said they were ; interestingly  the only three who had  changed position in some way ( sitting cross-legged / moving hair out of the eyes / smiling in the second photograph ) between the two photographs . The brain concentrates only on what it wants to . Here , one's own image leapt out to the exclusion of all else in the limited time available for viewing the photographs .
Similar behavior was exhibited when participants heard the pun , " the land of the rising sun/son " . Asked what kind of society it might describe , every participant but one came up with " a Japanese society " - a response clearly influenced by geograpy textbooks though the question was a sociological one . The solitary exception ( probably a student of sociology ) averred that it was certainly not a meritocracy . The brain tries to ease its workload by using readily available decoding devices ( in this case knowledge of geography or sociology directing perception ) whenever it can do so .  

Respondents heard the word " teapot " repeatedly and then the word " potty " several times , without any break in the repetition from beginning to end . When asked to identify the word that had just been repeated , more than half answered " teapot " . Only a little over a third caught the switch to a new word .
Respondents were also shown ten cue cards with the phrase , " the bear eats shoots and leaves " on the first nine and " the bear eats , shoots and leaves " on the last card . When asked to explain the sentence , every respondent but one said it described the bear's diet . The sole dissident volunteered that the last card seemed to speak about some kind of a cowboy bear . The change - i.e. the addition of a comma after the word " eats " - registered with just one respondent .
Taking a leaf out of the magician's manual , repetition was used to hide the trick - when observers are faced with repetition , they naturally assume that each repetition is identical . In this , they are encouraged to do so since the brain tends to try and anticipate future perceptions in trying to make sense of ambiguous input in a data-overloaded rapidly changing world .
Covert misdirection ( by a sigh to indicate fatigue with the repetition at the point when the change took place ; not memorable so as not to arouse suspicion ) , was used with half the sample . However , both halves largely overlooked the change in stimuli . People fail to notice that something is different from the way it was before even if it is staring them in the face - the brain , in cutting corners and making do , makes us change blind .
 
The mind moves in mysterious ways its wonders to perform . The more one studies it , the more one realises how much remains to be understood .
" What is mind ? No matter . What is matter ? Never mind . " ( Ascribed to Thomas H. Key ; 1799-1875 ) .