Introduction 5Mental rotation is defined as"the ability to rotate mental representations of two- dimensional and three-dimensional objects." [3] Notable research has shown that mental rotation is localised to the right cerebral hemispehere, the same place that is attributed to perception. Mental rotation goes through various cognitive stages like creating a mental object, rotating it till a comparison is made and finally 2decide if the objects are same or not. In this write up, we try to understand how the rotation mechanism works. Through a series of experiments, it has been shown that this rotation mechanism is essentially analog in nature, i.e. the object is rotated through all the intermediate forms till a comparison is made and we can't skip from one form to another. We describe the experiments below and try to understand the implications of the outcomes. And finally we shed some light upon the modern research on the topic. Shepard and 3Metzler (1971) They introduced the concept of mental rotation through this experiment, which has been extensively discussed in the class. They concluded that the mental process involves memtal imagery and their rotation through an analog mechanism. "The experimental results clearly supported this idea, because it was found that, for each subject, the time taken to confirm that both objects of a pair were, in fact, identical, increased in direct proportion to the angular rotational difference between them. It was as if the subjects were rotating their mental image at a steady rate (although this might be different for each subject), so that the further they had to go to bring their image into correspondence with the reference picture, the longer it would take them. On post-experimental questioning, most of the subjects confirmed that this was indeed how they believed that they had done the task."[1] It implied that the previously held belief, that thought processes involve only language (Behaviorist approach) was false and images also had a role to play in thought processes. The analog nature also created questions on the attempts of then Cognitive scientists to model human brain on a digital computer. However, Carpenter & Just, in 1978 came up with an alternate explanation for the linear graph discussed in the class. They proposed 4that the more a figure is rotated from its original orientation, the more number of eye movements a subject makes between the two images (due to the increased difference between the two concerned images), which leads to the linear graph and hence, we can't claim that the subject is rotating the images in an analog fashion. Source = Stanford Encyclopedia of Philosophy Cooper and Shepard 1973 Cooper and Shepard devised a series of experiments to counteract Carpenter and Just's claim. In this experiment of 1973, they used familiar 2D figures (usually letters of the alphabet or numbers), which eliminated the use of a second figure and hence there was no possibility of eye movements between two images influencing the test result. And the results were similar and they got a linear graph. Subjects rotated the canonical upright representation of the familiar figure (a representation of which they already have in their brain) and compared it to the given figure by rotating it through all the intermediate steps. This also showed that 2D and 3D rotations behaved similarly. Source = Stanford Encyclopedia of Philosophy Cooper 1975,1976 Cooper went a step further and used some irregular polygons in another experiment. Subjects were required to remember the shape of the polygons before the experiment started. They were also explicitly told to use rotation of remembered images to point out if an object was the same or its mirror image. It helped the use of rotation of 3imagery as a conscious experience under voluntary control, which was conclusive to prove the analog nature of mental rotation. Though there was the problem of 'experimental demand' (where subjects try to provide the answer they think the experimentalist wants, a well known problem in any psychological experiment). Source = Stanford Encyclopedia of Philosophy Mental rotation as a continuous mental transformation Through a series of three experiments [2], Shepard and Coopeer gave converging evidence that mental process is actually analog in nature. Expt1 Preceding a test character, cues about its 1orientation, identity or both were given. They found that neither alone had any remarkable effect on the performance of the subject. But given both and enough, the linear grapg ceased to exist. This ws similar to learning and association. Expt2 In this experiment, they controlled the putative rate of rotation of a subject with a series of tests. Then they asked them to rotate an object and used a probe mid-way and asked them to determine it's identity. They found out that the actual orientation of the probe was unimportant- but response time incresed 1monotonically with increasing angular distance from the presumed orientation. which supported an analog transformation mechanism. Expt3 Subjects had extensive practice in rotating an object in a single direction. Then they were tested with a probe rotated slightly away, say 190 degrees. The resulting graph 1had two peaks- one corresponding to counterclockwise rotation and the other for clockwise.1Thus it was the actual angular distance traversed by a rotation that determined the time consumed -- again consistent with an analog mechanism. Brain Mapping (Cohen et al. 1996) 2Activation in Brodmann's areas 7A and 7B, the middle frontal gyrus, extra-striate cortex, the hand somastosensory cortex, and frontal cortex Source- Wikipedia page Later developments [Parsons (1987)]: Embodiment effects (figures involving hand etc. ). Parsons showed that when figures of hand or other body parts were given to the subjects and they were asked to rotate them in mind, they had difficulty rotating the figures to a position which is physically impossible to do with one's own hands. This heralded the era of new research into other neural systems that might be involved during the rotation of an image ("finding suggested that the rotation of mental imagery was underlain by multiple neural systems: that is, (at least) a motoric/tactile one as well as a visual one") Hence, 3controversy continues about the underlying mechanisms of mental rotation. Links Presentation References [1] http://plato.stanford.edu/entries/mental-imagery/mental-rotation.html Explains the first three experiments [2] http://cognet.mit.edu/library/erefs/mitecs/tarr.html Gives a detailed explanation of Mental rotation as a continuous mental transformation [3] http://en.wikipedia.org/wiki/Mental_rotation Very good source for a gist