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If you're not thinking about the effects of handedness in your experiments, you may be drawing false conclusions from the data collected.
Handedness can bias results in some experiments. By reducing the effect of handedness bias (or in some circumstances, by exploiting it), you can draw more accurate conclusions from the data you collect.
Throughout this article you'll learn practical methods for assessing handedness and for reducing the risk of bias introduced by handedness effects.
Humans tend to be right-hand or left-hand dominant and generally display greater dexterity and more refined fine motor skills with their dominant hand. Where possible, humans also tend to prefer to use their dominant hand.
Similarly, laterality refers to the preference and dexterous dominance of one side of the body over the other (e.g., preferred foot for kicking a ball, forward foot on a bicycle, preferred eye for looking through a telescope, preferred ear for mobile phone). Laterality is not always consistent with handedness.
Simon and Rudell (1967) showed that the location of stimuli directly influences response-selection due to a natural tendency to react towards the source of the stimulation. Their conclusion was that stimulus location produces interference in a response-selection process. Therefore where stimulus location and response-selection are congruent, rather than incongruent, accuracy is greater and reaction times are faster.
This is known as the Simon effect.
Run a live demonstration experiment to test the Simon effect:
Exploiting the Simon effect in the design of machinery, tools, and human-computer interfaces leads to more intuitive and efficient solutions, and can significantly reduce human error.
The Edinburgh Handedness Inventory is a measurement for representing the handedness of a subject. The measurement is conducted by way of a short questionnaire. Responses given are used to calculate the Laterality Quotient of the subject.
The Edinburgh Handedness Inventory, originally devised by Oldfield (1971), has since been simplified by Veale (2013). The Edinburgh Handedness Inventory - Short Form (Veale, 2013) can be seen below (Figure 1).
Scoring the questionnaire is simply a matter of adding the answers together from each of the questions according to the table below
Finally, to calculate our Laterality Quotient, we take the questionnaire total and divide by 4.
|Left handed||-100 to -61|
|Mixed handed||-60 to 60|
|Right handed||60 to 100|
In general, when your experiments have large enough sample sizes for statistical power and when response allocation is randomized, any bias introduced by handedness will be washed out of your results. Randomizing response allocation involves randomizing button placement, randomizing key/value assignments, etc.
When two or more buttons are present, you can randomize their layout order from inside the editor (Figure 2) by selecting
For example, in Figure 2, two buttons are assigned:
When randomization is enabled, False will be randomly allocated to either leftmost or rightmost placement and True will be randomly allocated to one of the positions that remain (in this case there will be only one). Randomization remains consistent across all trials.
In order to maintain the same button order across multiple trial procedures and/or multiple trial blocks, you can clone a buttons response on the trials timeline to keep a consistent layout across all buttons. So for example, if a randomized button layout produced the layout as seen in Figure 2 above (False on the left, True on the right) every
Response - buttons in every trial block and trial procedure in the entire experiment will contain the same layout (False left, True right) when using a clone.
Response - buttonstype (Figure 3)
Clone (from a different procedure)creation option (Figure 3)
When two or more keys are present, you can randomize their key/value assignments from inside the editor (Figure 5) by selecting
For example, in Figure 5, two keys are assigned:
When randomization is enabled, f will be randomly allocated to either left or right and j will be randomly allocated to one of the values that remain (in this case there will be only one). Randomization remains consistent across all trials.
In order to maintain the same key/value assignments across multiple trial procedures and/or multiple trial blocks, you can clone a keyboard response on the trials timeline to keep consistent key/value assignments across all keyboard responses. So for example, if a randomized key/value assignment produced the assingments as (f = left, j = right) every
Response - keyboard in every trial block and trial procedure in the entire experiment will contain the same key/value assignments (f = left, j = right) when using a clone.
Response - keyboardtype (Figure 6)
Clone (from a different procedure)creation option (Figure 6)