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Title: The role of category structure in processing visual stimulus dimensions

Ethics approval: 2011-117

Researchers:
Jon Prince
David Ahmed
Casey Reeve
Keegan Wilder-Bass
Sigourney Lenihan
Melai Chen
Aida Durakovic

Background and Research Aims

We as humans are constantly surrounded by information from the environment such as colours, words, and other similar properties that require the brain to individually process and sort these pieces of information so that it makes sense. How the brain takes in these multiple pieces of information and assembles them into one clear context remains an unanswered and complex issue in psychology, and is known as the ‘binding problem’. A relatively unexplored area of this binding problem is how changing the prototypicality (how typical or normal) of one of these pieces of information, might interfere with our ability to process an entirely different one. The current study was set up to investigate whether or not changing the prototypicality of one structure will affect the ability to correctly classify another. For this study, words and colours were selected as the stimuli to change and observe. It was predicted that varying prototypicality in either a word or colour task would not significantly interfere with the ability to correctly classify either words or colours. It was also predicted that non-prototypical non-words (e.g. words that are not real XLGJG) would be responded to the fastest out of all the word conditions.

Experiment

The participants in the current study consisted of psychology students from Murdoch University in West Australia. Participants underwent two types of classification tasks; a lexical decision in which they were asked to identify whether or not the presented letters on the computer screen formed a word, or whether it was not a word (non-word), and a colour task, in which they were asked to identify whether or not the presented colour on the screen was red or green. There were four conditions of words, and four conditions of colour, of which two were considered typical or common, and the other two were not. A total of 384 trials were presented in this experiment. In the lexical decision task, prototypical words were selected based on how common they were (e.g. apple), and the not so common words (non -prototypical), were based on the fact they were uncommon (e.g. stork). Unidentifiable words (non-prototypical non-words such as ZLMON) were used, as well as words that mimicked proper words (the non-prototypical nonwords such as ‘Berch’). The colour task involved identifying either the colour green or red infused in one of the presented words. One of the greens and one of the reds was prototypical (a general green or red), whist another green and red were non-prototypical (a not so common looking red or green).

Results

Varying the prototypicality of stimuli did not significantly affect the ability of participants in correctly classifying either stimuli of words or colours in the colour task or lexical decision task, supporting the first prediction of the study. The second prediction was also supported as the results showed that the non-prototypical non-word condition received the fastest responses in comparison to any of the other word conditions. One interesting finding was that prototypical red was responded significantly faster than the non-prototypical red. This may be due to the fact that the colour red plays some significant roles in society (e.g. such as warning signs like stop signs) and therefore we recognise this colour much easier. Also, there was an interaction between the non-prototypical non-word in the colour task by which accuracy was quite low when identifying the colour of the word. This is an anomalous result given the majority of previous literature available suggesting that words interfere with the processing of colour, not the other way around, yet why this happened remained unclear. Ultimately, it is hoped that these findings from the current study can guide future work on how we combine information (such as colour and word) and increase our understanding of the binding problem.

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