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Why We See Randomness Correctly

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Given one specific result of tossing a coin a finite number of times, the probability of observing a streak is actually less than that of observing a specific nonstreak.

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									Attention, Perception, & Psychophysics
2009, 71 (5), 985-987
doi:10.3758/APP.71.5.985



                                            News From the Field
   PROBABILITY PERCEPTION                           Experiments on attention and psy-       the likelihood of such movements. Of
                                                 chophysics often require observers         course, in cases where precise fixation
Why We See Randomness
                                                 to maintain fixation to ensure that        must be maintained, as when making
Correctly                                        the results are due to covert atten-       electrophysiological recordings, gaze
Hahn & Warren (2009). Perceptions of ran-        tion or to effects at a specific reti-     monitoring will be required. However,
domness: Why three heads are better than four.
Psychol Rev, 116, 454.                           nal locus. Unfortunately, the typical      using fixation training can minimize
                                                 solutions for minimizing eye move-         the amount of data lost to errant sac-
   Kahneman and Tversky (1972,                   ments can be problematic. Eyetrack-        cades. —S.P.V.
Cogn Psych 3:430) convincingly                   ers are costly (and underutilized if
demonstrated that people incorrectly             only used to monitor gaze position),         EARLY SPEECH PERCEPTION
perceive the randomness of events.               and brief timing parameters are not
Given all possible results of tossing            always feasible when studying cer-         Separating the Wheat
a coin, the likelihood of observing a            tain phenomena.                            From the Chaff
streak of four heads (HHHH) and a                   Enter a potential solution: Train       Best et al. (2009). Development of phono-
specific nonstreak (e.g., HHHT) are              observers to maintain f ixation.           logical constancy: Toddlers’ perception of
the same. Most people incorrectly                                                           native- and Jamaican-accented words. Psychol
                                                 Guzman-Martinez et al. did exactly         Sci, 20, 539.
judge the streak to be less likely.              this by showing observers random dot
Hahn and Warren argue, however,                  displays. The display flickered, with         As children begin to acquire a spo-
that given the experience that people            all black pixels becoming white, and       ken language, such as English, they
have of random events, this judgment             vice versa. When observers main-           must learn which differences in pro-
is not only reasonable, but correct!             tained fixation, the display appeared      nunciation matter, and which don’t,
Given one specific result of tossing             to be uniformly gray because of per-       in order to understand spoken words.
a coin a finite number of times, the             ceptual averaging; if their eyes moved,    Differences in dialects and accents, in
probability of observing a streak is             they perceived instead a black-and-        particular, can significantly change the
actually less than that of observing a           white pattern. To train fixation, the      way spoken words are produced, and
specific nonstreak. The probability of           authors first had observers perform        children must undercover what prop-
observing HHHH in a given set of 20          
								
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