Illusory conjunctions are psychological concepts where participants accidentally combine features of two objects into one object. There are both visual illusory conjunctions and auditory illusory conjunctions. Both types occur due to a lack of attention. Visual attention depends on fixation and amount of time allotted to focus on an object. With a short span of time to interpret an object, blending of different aspects in a visual field, like shapes and colors, can occasionally be skewed which results in visual illusory conjunctions. For example a study designed by Anne Treisman and Schmidt, required participants to see a visual presentation of black numbers and shapes in different colors. Some shapes were larger than others but all shapes and numbers were evenly spaced and shown for 200 ms. Due to the fact that the shapes and numbers were shown for such a short amount of time, when the participants were asked to recall them they reported answers such as a small green triangle instead of a small green circle. If the space is smaller between objects illusory conjunctions happen more often.
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Along with the feature integration the location formed from the two objects is a combined result of their locations, but the similarity of the features is what increases the likelihood of an illusory conjunction.[1] In order for an illusory conjunction to occur the two objects that are not the focus of attention need to be within the visual field. The closer two objects are the more likely the illusory conjunction to occur [2] The increased likelihood of an inllusory conjunction to occur when the objects are closer together may be due to the difference in processing when the objects are more distant from each other. One theory supports that this decrease in illusory conjunctions with increased distance between objects is due to the use of bihemispheric input processing making closer objects more likely to be conjuncted because only one of the cerebral hemispheres sees and processes both objects involved in an illusory conjunction.[3] Although proximity increases the likelihood of an illusory conjunction, illusory conjunctions formed between objects occur often even when the objects are distant, though still within the attentional field. When objects are outside of attention in order for an illusory conjunction to occur they must be adjacent to each other to combine features.[4] Objects become more susceptible to illusory conjunction not only due to relation to each other, but also in relation to the density of objects in the attentional location. As the density of objects increases attention divides more increasing the possibility of the formation of an illusory conjuncntion.[5]
Illusory conjunctions can occur even when all the stimuli involved is not present. Physical stimuli and images can be combined through a lapse in memory of an image that is filled by physical stimuli [6] Illusory conjunctions often occur through memory errors because the situations in which illusory conjunctions happen involve multiple tasks or tasks that commonly divid a person's attention.[7] While memory errors can aid in the formation of illusory conjunctions their formation is not dependent on memory errors.[8] These memory errors can be caused by a multitude of attentional and recall issues. The density of objects is important for object location along with recognition errors because as the number of objects in a space increases the amount of things to be processed and stored to memory increases. This increase in objects creates a prime situation for memory to lapse and form an illusory conjunction.[9]
Auditory illusory conjunctions occur in a similar manner to visual illusory conjunctions, when hearing different sounds one sound is perceived by the individual. An example of auditory illusory conjunctions is the octave illusion. During this study participants heard different tones one high and one low. One was played in the right ear and the other in the left ear. The tones were played at exactly the same time for 20 seconds. When asked what the participant heard they reported one tone changing in frequency and location. Limited time caused an auditory illusory conjunction for the participants.[10] Illusory conjunctions occur, both visually and auditory, due to lack of time to focus ones attention to the objects or sounds and perceive them correctly, therefore combining features of different objects. Auditory stimuli can also form an illusory conjunction through the combination of a pitch and tones. The greater the number of tones involved in a sequence the greater the likelihood of an illusory conjunction to occur with a different pitch and a tone.[11] Illusory conjunctions spread to more than just auditory and visual stimuli. Illusory conjunctions occur through touch also. This happens when a seen object is attributed textures that someone is feeling. This phenomenon is also more common when only one of the cerebral hemispheres is perceiving and processing the visual and tactile stimuli.[12]
There is some debate as to whether or not illusory conjunctions exist as a psychological phenomenon. The main criticism is that research in support of illusory conjunctions is not sufficient enough in the methods used to analyze the data. If this criticism were found to be true it would support the theory that illusory conjunctions are only illusions and nothing more [13] It has also been found in a few studies that two objects that are not the focus of attention are also more likely to be combined when they are adjacent to each other. Although it would seem more common for objects to combine when they are not the focus of attention it is more likely for an illusory conjunction to occur when objects are the focus of attention [14] Illusory conjunctions can occur in long and brief exposure times along with the different levels of attention paid to the objects involved.[15]
Anne Treisman: http://psych.princeton.edu/psychology/research/treisman/index.php Optical Illusions: http://www.acnr.co.uk/pdfs/volume6issue2/v6i2visual.pdf