Squinting with the mind's eye: effects of stimulus resolution on imaginal and perceptual comparisons

Applications of Alpha Neurofeedback Processes for Enhanced Mental Manipulation of Unfamiliar Molecular and Spatial Structures

This study explores a novel approach to enhancing cognitive proficiency by targeting neural mechanisms that facilitate science and math learning, especially mental rotation. The study specifically examines the relationship between upper alpha intensity and mental rotation skills. Although prior neurofeedback research for increasing upper alpha highlights this correlation, mostly with familiar objects, novel chemistry and math learning prompts envisioning unfamiliar objects which question the persistence of this correlation. This study revisits the upper alpha and mental rotation relationship in the context of unfamiliar objects with a single neurofeedback session and examines the efficiency of manual and automatic neurofeedback protocols. Results will provide a basis for integrating neurofeedback protocols into learning applications for enhanced learning. Our study encompassed three cohorts: Group 1 experienced an automatic neurofeedback protocol, Group 2 received a manual neurofeedback protocol, and the control group had no neurofeedback intervention. The experimental phases involved EEG measurement of individual upper alpha (frequency of maximal power + 2 Hz) intensity, mental rotation tasks featuring geometric and unfamiliar molecular stimuli, one neurofeedback session for applicable groups, post-treatment upper alpha level assessments, and a mental rotation retest. The neurofeedback groups exhibited increased levels of upper alpha power, which was correlated with improved response time in mental rotation, regardless of stimulus type, compared to the control group. Both neurofeedback protocols achieved comparable results. This study advocates integrating neurofeedback into learning software for optimal learning experiences, highlighting a single session's efficacy and the substantial neurofeedback protocol's impact in enhancing upper alpha oscillations.

Neurofunctional Symmetries and Asymmetries during Voluntary out-of- and within-Body Vivid Imagery Concurrent with Orienting Attention and Visuospatial Detection

We explored whether two visual mental imagery experiences may be differentiated by electroencephalographic (EEG) and performance interactions with concurrent orienting external attention (OEA) to stimulus location and subsequent visuospatial detection. We measured within-subject (N = 10) event-related potential (ERP) changes during out-of-body imagery (OBI)—vivid imagery of a vertical line outside of the head/body—and within-body imagery (WBI)—vivid imagery of the line within one’s own head. Furthermore, we measured ERP changes and line offset Vernier acuity (hyperacuity) performance concurrent with those imagery, compared to baseline detection without imagery. Relative to OEA baseline, OBI yielded larger N200 and P300, whereas WBI yielded larger P50, P100, N400, and P800. Additionally, hyperacuity dropped significantly when concurrent with both imagery types. Partial least squares analysis combined behavioural performance, ERPs, and/or event-related EEG band power (ERBP). For both imagery types, hyperacuity reduction correlated with opposite frontal and occipital ERP amplitude and polarity changes. Furthermore, ERP modulation and ERBP synchronizations for all EEG frequencies correlated inversely with hyperacuity. Dipole Source Localization Analysis revealed unique generators in the left middle temporal gyrus (WBI) and in the right frontal middle gyrus (OBI), whereas the common generators were in the left precuneus and middle occipital cortex (cuneus). Imagery experiences, we conclude, can be identified by symmetric and asymmetric combined neurophysiological-behavioural patterns in interactions with the width of attentional focus.

Pictorial low-level features in mental images: evidence from eye fixations

It is known that eye movements during object imagery reflect areas visited during encoding. But will eye movements also reflect pictorial low-level features of imagined stimuli? In this paper, three experiments are reported in which we investigate whether low-level properties of mental images elicit specific eye movements. Based on the conceptualization of mental images as depictive representations, we expected low-level visual features to influence eye fixations during mental imagery, in the absence of a visual input. In a first experiment, twenty-five participants performed a visual imagery task with high vs. low spatial frequency and high vs. low contrast gratings. We found that both during visual perception and during mental imagery, first fixations were more often allocated to the low spatial frequency-high contrast grating, thus showing that eye fixations were influenced not only by physical properties of visual stimuli but also by its imagined counterpart. In a second experiment, twenty-two participants imagined high contrast and low contrast stimuli that they had not encoded before. Again, participants allocated more fixations to the high contrast mental images than to the low contrast mental images. In a third experiment, we ruled out task difficulty as confounding variable. Our results reveal that low-level visual features are represented in the mind's eye and thus, they contribute to the characterization of mental images in terms of how much perceptual information is re-instantiated during mental imagery.

Meta-analytic comparison of trial- versus questionnaire-based vividness reportability across behavioral, cognitive and neural measurements of imagery

Vividness is an aspect of consciousness related to mental imagery and prospective episodic memory. Despite being harshly criticized in the past for failing to demonstrate robust correlations with behavioral measures, currently this construct is attracting a resurgent interest in cognitive neuroscience. Therefore, an updated examination of the validity of this construct is timely. A corpus of peer-reviewed literature was analyzed through meta-analysis, which compared the two main formats used to measure vividness [trial-by-trial vividness ratings (VR) and the Vividness of Visual Imagery Questionnaire (VVIQ)]. These two formats were compared in relation to all available behavioral/cognitive (BC) and neuroscience (NS) measures in Phase 1 (3542 statistical observations representing 393 journal articles); and then in relation to all available BC, EEG and fMRI literature in Phase 2 (3624 observations representing 402 articles). Both Phases observed significantly larger effect size estimates (ESEs) for VR than VVIQ, and larger ESEs for NS than BC measures. ESEs for EEG and fMRI were not significantly different in Phase 2, but were greater than BC ESEs. These data suggest VR are a more reliable self-report measure than VVIQ, and may reflect a more direct route of reportability than the latter. Furthermore, both VR and VVIQ are more strongly associated with the neural, than the cognitive and behavioural correlates of imagery. If one establishes neuroscience measures as the criterion variable, then self-reports of vividness show higher construct validity than behavioural/cognitive measures of imagery. We discuss how the present findings contribute to current issues on measurement of reportability; and how this study advances our understanding of vividness as a phenomenological characteristic of imagery, and other forms of conscious experience which do not necessarily involve imagery.

Neurofunctional correlates of environmental cognition: an FMRI study with images from episodic memory

This study capitalizes on individual episodic memories to investigate the question, how dif-ferent environments affect us on a neural level. Instead of using predefined environmental stimuli, this study relied on individual representations of beauty and pleasure. Drawing upon episodic memories we conducted two experiments. Healthy subjects imagined pleasant and non-pleasant environments, as well as beautiful and non-beautiful environments while neural activity was measured by using functional Magnetic Resonance Imaging. Although subjects found the different conditions equally simple to visualize, our results revealed more distribut-ed brain activations for non-pleasant and non-beautiful environments than for pleasant and beautiful environments. The additional regions activated in non-pleasant (left lateral prefrontal cortex) and non-beautiful environments (supplementary motor area, anterior cortical midline structures) are involved in self-regulation and top-down cognitive control. Taken together, the results show that perceptual experiences and emotional evaluations of environments within a positive and a negative frame of reference are based on distinct patterns of neural activity. We interpret the data in terms of a different cognitive and processing load placed by exposure to different environments. The results hint at the efficiency of subject-generated representations as stimulus material.

How visual short-term memory maintenance modulates the encoding of external input: evidence from concurrent visual adaptation and TMS

The impact of memory representations on the encoding of visual input has been the subject of much debate. Here we investigated this issue by examining how visual short-term memory (VSTM) maintenance of orientation information modulates the strength of the tilt aftereffect (TAE) induced by a concurrent visual adapter. We reasoned that if VSTM maintenance facilitates visual processing of stimuli that match the VSTM content, then the magnitude of the TAE should be enhanced when the orientations of the memory item and the adapter are identical. In contrast, if VSTM content inhibits visual processing, then the TAE induced by the adapter should be reduced. Our results are consistent with the latter hypothesis, and a TMS study demonstrated that the reduction of the TAE by VSTM maintenance of orientation information occurs in the early visual cortex. VSTM maintenance of shape information also reduced the TAE magnitude, but to a smaller extent than maintenance of orientation information. A TMS experiment did not implicate the early visual cortex in this phenomenon. In summary, our results indicate that VSTM maintenance under these circumstances inhibits the encoding of concurrent visual input, and that this inhibition occurs at various levels of the visual cortex.

Similar Effects of Visual Perception and Imagery on Simple Reaction Time

A longstanding issue is whether perception and mental imagery share similar cognitive and neural mechanisms. To cast further light on this problem, we compared the effects of real and mentally generated visual stimuli on simple reaction time (RT). In five experiments, we tested the effects of difference in luminance, contrast, spatial frequency, motion, and orientation. With the intriguing exception of spatial frequency, in all other tasks perception and imagery showed qualitatively similar effects. An increase in luminance, contrast, and visual motion yielded a decrease in RT for both visually presented and imagined stimuli. In contrast, gratings of low spatial frequency were responded to more quickly than those of higher spatial frequency only for visually presented stimuli. Thus, the present study shows that basic dependent variables exert similar effects on visual RT either when retinally presented or when imagined. Of course, this evidence does not necessarily imply analogous mechanisms for perception and imagery, and a note of caution in such respect is suggested by the large difference in RT between the two operations. However, the present results undoubtedly provide support for some overlap between the structural representation of perception and imagery.

Working memory and acquisition of implicit knowledge by imagery training, without actual task performance

This study investigated acquisition of a mirror-reading skill via imagery training, without the actual performance of a mirror-reading task. In experiment I, healthy volunteers simulated writing on an imaginary, transparent screen placed at eye level, which could be read by an experimenter facing the subject. Performance of this irrelevant motor task required the subject to imagine the letters inverted, as if seen in a mirror from their own point of view (imagery training). A second group performed the same imagery training interspersed with a complex, secondary spelling and counting task. A third, control, group simply wrote the words as they would normally appear from their own point of view. After training with 300 words, all subjects were tested in a mirror-reading task using 60 non-words, constructed according to acceptable letter combinations of the Portuguese language. Compared with control subjects, those exposed to imagery training, including those who switched between imagery and the complex task, exhibited shorter reading times in the mirror-reading task. Experiment II employed a 2 x 3 design, including two training conditions (imagery and actual mirror-reading) and three competing task conditions (a spelling and counting switching task, a visual working memory concurrent task, and no concurrent task). Training sessions were interspersed with mirror-reading testing sessions for non-words, allowing evaluation of the mirror-reading acquisition process during training. The subjects exposed to imagery training acquired the mirror-reading skill as quickly as those exposed to the actual mirror-reading task. Further, performance of concurrent tasks together with actual mirror-reading training severely disrupted mirror-reading skill acquisition; this interference effect was not seen in subjects exposed to imagery training and performance of the switching and the concurrent tasks. These results unequivocally show that acquisition of implicit skills by top-down imagery training is at least as efficient as bottom-up acquisition.

Reality monitoring in hypnosis: a real-simulating analysis

The extent to which hypnotic suggestions are perceived as real is central to understanding hypnotic response. This study indexed the reality attributed to hypnotic suggestion through subtle projection of a visual image during simultaneous suggestion for a visual hallucination that resembled the projected image. Twenty real hypnotized and 20 simulating nonhypnotized participants were administered a hypnotic induction and given a suggestion to hallucinate a shape, and then the projected image was introduced. Following the hypnosis session, an Experiential Analysis Technique was employed to index experiential responses. Real, but not simulating, participants made comparable reality ratings when the projected image was absent and present. Reals, but not simulators, also reported more effort in maintaining belief in the suggestion when the projection was absent. These findings suggest that the reality attributed to a hypnotic suggestion cannot be attributed to demand characteristics.

Cognitive basis of hallucinations in schizophrenia: role of top-down information processing

Hallucinations in schizophrenia have been regarded to result from the erroneous attribution of internally generated information to an external source. Distortions in mental imagery may underlie such confusions. We investigated performance of 77 subjects on multiple behavioral measures of auditory and visual mental imagery and perception, and a measure of reality monitoring. Comparisons were made between performance of schizophrenia patients with (N=22) and without (N=35) hallucinations and matched normal comparison subjects (N=20), after controlling for attentional factors. No differences emerged on any of the mental imagery measures, nor on reality monitoring accuracy. This suggests that there is no stable disposition towards abnormal mental imagery associated with hallucinations. However, for patients with active hallucinations (N=12), hallucination severity correlated positively with a measure of imagery-perception interaction in the auditory modality, r=0.70, p=0.01. Although preliminary, this finding is consistent with recent theoretical proposals in which hallucinations have been suggested to result from an increased influence of top-down sensory expectations on conscious perception.

Seeing is believing: the reality of hypnotic hallucinations

Two experiments investigated the reality attributed to hypnotic suggestion through subtle projection of a visual image during simultaneous suggestion for a visual hallucination that resembled the projected image. In Experiment 1, high and low hypnotizable participants were administered either a hypnotic induction or wake instructions, given a suggestion to hallucinate a shape, and then the projected image was subsequently introduced. Although highs in both conditions rated the projected image more vividly than lows, highs in the hypnosis (but not wake) condition made comparable reality ratings when the projected image was absent and present. In Experiment 2, high hypnotizable participants were administered a suggestion to see a shape on a wall. For half the participants the suggested image was projected on the wall and then removed, and for half the projection was initially absent and then introduced. Participants who had the projection absent and then present reported comparable reality and vividness ratings when the projection was absent and present. These findings indicate that elevated hypnotizability and hypnosis are associated with attributions of external reality to suggested experiences.

Mental image generation and the contrast sensitivity function

In one experiment, observers were instructed to generate small and large visual mental images in a light-adapted or a dark-adapted viewing condition, and to rate the vividness of each image. In light-adapted viewing, small images were generated faster than large images. However, the pattern of results was reversed in dark-adapted viewing. Furthermore, the dark-adapted images were more vivid than the light-adapted images. The results show that mental images can be mapped onto some regions of the contrast sensitivity function (CSF), so that the latency (and vividness) of a particular image can be predicted. Since the CSF reflects visual processes occurring mainly in V1, the results agree with functional magnetic resonance imaging data in indicating that early visual pathways participate in imagery. Nonetheless, imagery and perception may involve different processes hosted by the same neural structures as indicated by the direct relationship between image latency and contrast sensitivity.

Mental imagery of high- and low-resolution gratings activates area 17

Some, but not all, previous neuroimaging studies of visual mental imagery have found that Area 17 (primary visual cortex) is activated when people visualize objects. The present study was designed to test the hypothesis that the necessary degree of resolution of the mental image is a determining factor in whether Area 17 is activated during imagery. Eight male subjects visualized and compared sets of stripes that required high or low resolution to resolve, while their brains were scanned using 15O(CO2) positron emission tomography (PET). When imagery in general (visualization of high- and low-resolution gratings stimuli combined) was compared to an auditory baseline condition where subjects did not visualize, Area 17 was activated. However, region of interest (ROI) and statistical parametric mapping (SPM) analyses revealed no difference between imagery conditions using high- and low-resolution stimuli. These results indicate that the resolution of the stimuli alone does not necessarily determine whether Area 17 will be activated during visual mental imagery.

Mental imagery and perception in hallucination-prone individuals

College students screened for hallucination-proneness using the Launay-Slade Hallucination Scale (LSHS) were compared on measures of self-report vividness of imagery and on behavioral measures of imagery and perception (visual and auditory). Specifically, we tested the hypothesis whether hallucination-prone individuals would show smaller differences between imagery and perception performance, which may be indicative of increased sensory characteristics of mental images. We replicated earlier findings of higher self-report imagery ratings in the high hallucination-prone group. However, the two groups did not differ on five of six behavioral imagery-perception comparisons. On one visual task, hallucination-proneness was associated with larger imagery-perception differences. Our results reveal a dissociation between the level of subjective experience and the information processing level. Although vividness of mental images may be subjectively associated with mild hallucinatory experiences, we suggest that cognitive processes associated with reality discrimination rather than increased perceptual characteristics of mental images may play a role at the information processing level.

Mental imagery of faces and places activates corresponding stiimulus-specific brain regions

What happens in the brain when you conjure up a mental image in your mind's eye? We tested whether the particular regions of extrastriate cortex activated during mental imagery depend on the content of the image. Using functional magnetic resonance imaging (fMRRI), we demonstrated selective activation within a region of cortex specialized for face perception during mental imagery of faces, and selective activation within a place-selective cortical region during imagery of places. In a further study, we compared the activation for imagery and perception in these regions, and found greater response magnitudes for perception than for imagery of the same items. Finally, we found that it is possible to determine the content of single cognitive events from an inspection of the fMRI data from individual imagery trials. These findings strengthen evidence that imagery and perception share common processing mechanisms, and demonstrate that the specific brain regions activated during mental imagery depend on the content of the visual image.