Mental imagery and emotion: a special relationship? Imagery led to a greater increase in anxiety. Hallucinations in schizophrenia are defined as mental experiences believed to be external percepts. event increases its perceived likelihood of occurrence [. A mental image or mental picture is the representation in a person's mind of the physical world The concept of "the mind's eye" first appeared in English in Chaucer's (c. in terms of verbal codes—finding words that define them or describe them. . Thus, the neural substrates of visual imagery and perception overlap in. between visual mental imagery and perception; these stud- ies have . objects, then we would expect a high correlation between .. One explanation for this.
Participants were asked to maintain fixation to avoid the experience of the flash. All participants reported noticing the effect and using it as feedback to improve fixation.
After the main fMRI experiment, each participant performed 5 localizer runs duration s each to identify category-selective regions for bodies, places, and houses, as well as high-level cortex that responds more to pictures of objects than to scrambled counterparts without a clear category preference.
Participants viewed blocks of images from 5 different stimulus classes bodies, faces, scenes, houses, everyday objects, and grid-scrambled objects. In each run, 2 blocks of images from each of the 5 different stimulus classes were shown, that is, in total 10 image blocks.
Blocks of images were interleaved with s periods of a uniform black background. Each image block had a duration of 16 s and consisted of 20 images presentation time ms, ms gap. To preclude a foveal bias in the cortical activation, the same picture was presented simultaneously at 3 adjacent positions along the horizontal meridian. Participants were asked to maintain fixation on a central fixation dot.
Mental Imagery (Stanford Encyclopedia of Philosophy)
Participants performed a one-back task on repetitions of an image in order to sustain attention to the images. In each block, at random 4 of the 20 images were repeated. Participants indicated their answer via a button press. The serial order of conditions was counterbalanced within participants. Finally, 10 out of the 16 participants participated in a retinotopic mapping session to identify low-level visual regions V1, V2, and V3 using the standard travelling wave method with a double wedge and expanding ring stimuli Sereno et al.
Participants completed 3—4 runs of angular mapping to map the boarders between visual regions and 2—3 runs of eccentricity mapping. Gray matter segmentation of anatomical images was conducted using FreeSurfer Dale et al. We defined the borders between ventral and dorsal areas V1, V2, and V3 by visual inspection of flattened polar angle maps. Eccentricity maps were used to check whether anterior limits of the regions as defined by polar angle maps corresponded with eccentricity mapping.
Borders of areas V1, V2, and V3 could be reliably defined in all 10 participants bilaterally. The regions of interest ROIs for visual areas V1 to V3 were based on the borders on the flattened surface and transformed back into the functional space of the main experiment. For the main experiment, 5 runs of volumes were acquired for each participant gradient-echo echo-planar imaging [EPI] sequence: Slices were positioned parallel to the temporal lobe, such that the fMRI volume covered the ventral visual regions from low-level visual to anterior temporal cortex.
For the 5 localizer scans, consisting of 90 volumes each, the parameters were identical. For the retinotopic mapping, 6 to 8 runs of volumes were acquired for each participant gradient-echo EPI sequence: The slices were positioned parallel to the calcarine sulcus.
Data were realigned and slice-time corrected. In the following, we will first describe the analysis of the functional localizers that served the definition of ROIs.
We then explain the analysis of the main experiment. The data were modeled with a general linear model GLM that included the 5 stimulus classes as conditions faces, places, bodies, objects and scrambled objects. Next, we identified voxels that showed category preference by contrasting parameter estimates evoked by the specific category in question with parameter estimates evoked by objects.
Next, we defined regions of interest ROIs in a multistep process. Then, we defined a sphere with a 7-voxel radius around this peak voxel. This step limited further voxel selection by vicinity to the most activated voxel and by anatomical location.
Finally, within this sphere, we selected only the most activated voxels in each contrast. This yielded up to 12 category-selective ROIs in each subject: All areas were defined in the right and the left hemisphere, respectively.
In addition, up to 4 object-selective ROIs were identified in the same fashion: In total, we identified the following numbers of ROIs: Importantly, our ROI identification procedure takes into account individual differences in the location of category-selective regions and guarantees equality of ROI size across ROIs and subjects. Finally, we selected voxels in low-level visual regions V1, V2, and V3 as defined by retinotopic mapping.
As each lower-level visual region could be defined in each participant, we identified 20 ROIs for V1, V2, and V3 each. Thus, no fMRI data were rejected from further analysis. We modeled the cortical response to the experimental conditions in the main experiment for each run separately. For this, we treated all exemplars belonging to the same category as the same condition. The onsets and durations of the stimulus presentations were entered into a GLM as regressors and convolved with a hemodynamic response function.
The estimation of this model yielded 16 parameter estimates per run, representing the responsiveness of each voxel to the 4 different object categories at either of the 2 different locations in either the perception or the imagery condition.
Pattern Classification Data from the main experiment were subjected to 2 multivoxel pattern classification analyses Muller et al.
The 2 analyses investigated whether imagery and perception share representations of 1 object category and 2 object location. Each analysis shared a basic framework that was adapted.
Analyses were conducted independently for each ROI and for each subject. Please recall that ROIs were defined based on the independent localizer runs.
For each run, we extracted parameter estimates for the experimental conditions under investigation see below. These parameter estimates constituted the pattern vectors length ofcorresponding to voxels that entered the pattern classification.
Pattern vectors from 4 out of 5 runs were assigned to a training data set, which was used to train the SVC. The trained SVC was used to classify pattern vectors from the independent test data set consisting of the fifth run.
As an example of introspection, it demonstrates that the internal life of the mind rarely came into focus in literature until the introspective realism movement in the 19th century. Physical basis[ edit ] The biological foundation of the mind's eye is not fully understood.
Studies using fMRI have shown that the lateral geniculate nucleus and the V1 area of the visual cortex are activated during mental imagery tasks. The visual pathway is not a one-way street. Higher areas of the brain can also send visual input back to neurons in lower areas of the visual cortex. For example, PET scans have shown that when subjects, seated in a room, imagine they are at their front door starting to walk either to the left or right, activation begins in the visual association cortexthe parietal cortexand the prefrontal cortex - all higher cognitive processing centers of the brain.
The thalamus has been found to be discrete to other components in that it processes all forms of perceptional data relayed from both lower and higher components of the brain. Damage to this component can produce permanent perceptual damage, however when damage is inflicted upon the cerebral cortexthe brain adapts to neuroplasticity to amend any occlusions for perception. It can be thought that the neocortex is a sophisticated memory storage warehouse in which data received as an input from sensory systems are compartmentalized via the cerebral cortex.
This would essentially allow for shapes to be identified, although given the lack of filtering input produced internally, one may as a consequence, hallucinate - essentially seeing something that isn't received as an input externally but rather internal i.
Not all people have the same internal perceptual ability. For many, when the eyes are closed, the perception of darkness prevails. However, some people are able to perceive colorful, dynamic imagery. The use of hallucinogenic drugs increases the subject's ability to consciously access visual and auditory, and other sense percepts. Furthermore, the pineal gland is a hypothetical candidate for producing a mind's eye; Rick Strassman and others have postulated that during near-death experiences NDEs and dreamingthe gland might secrete a hallucinogenic chemical N,N-Dimethyltryptamine DMT to produce internal visuals when external sensory data is occluded.
The hypothesized condition where a person lacks a mind's eye is called aphantasia. The term was first suggested in a study. Another is of the pictures summoned by athletes during training or before a competition, outlining each step they will take to accomplish their goal.
Calling up an image in our minds can be a voluntary act, so it can be characterized as being under various degrees of conscious control. According to psychologist and cognitive scientist Steven Pinker our experiences of the world are represented in our minds as mental images. These mental images can then be associated and compared with others, and can be used to synthesize completely new images.
- Mental Imagery
In this view, mental images allow us to form useful theories of how the world works by formulating likely sequences of mental images in our heads without having to directly experience that outcome. Whether other creatures have this capability is debatable. There are several theories as to how mental images are formed in the mind. These include the dual-code theorythe propositional theory, and the functional-equivalency hypothesis. The dual-code theory, created by Allan Paivio inis the theory that we use two separate codes to represent information in our brains: Image codes are things like thinking of a picture of a dog when you are thinking of a dog, whereas a verbal code would be to think of the word "dog".
When abstract words are thought of, it is easier to think of them in terms of verbal codes—finding words that define them or describe them.