When is early visual cortex activated during visual mental imagery?

Although many neuroimaging studies of visual mental imagery have revealed activation in early visual cortex (Areas 17 or 18), many others have not. The authors review this literature and compare how well 3 models explain the disparate results. Each study was coded 1 or 0, indicating whether activation in early visual cortex was observed, and sets of variables associated with each model were fit to the observed results using logistic regression analysis. Three variables predicted all of the systematic differences in the probability of activation across studies. Two of these variables were identified with a perceptual anticipation theory, and the other was identified with a methodological factors theory. Thus, the variability in the literature is not random.     

Revision: is visual perception a requisite for visual imagery?

Vision is the most highly developed sense in man and represents the doorway through which most of our knowledge of the external world arises. Visual imagery can be defined as the representation of perceptual information in the absence of visual input. Visual imagery has been shown to complement vision in this acquisition of knowledge--it is used in memory retrieval, problem solving, and the recognition of properties of objects. The processes underlying visual imagery have been assimilated to those of the visual system and are believed to share a neural substrate. However, results from studies in congenitally and cortically blind subjects have opposed this hypothesis. Here I review the currently available evidence.     

How parallel is visual processing in the ventral pathway?

Visual object perception is usually studied by presenting one object at a time at the fovea. However, the world around us is composed of multiple objects. The way our visual system deals with this complexity has remained controversial in the literature. Some models claim that the ventral pathway, a set of visual cortical areas responsible for object recognition, can process only one or very few objects at a time without ambiguity. Other models argue in favor of a massively parallel processing of objects in a scene. Recent experiments in monkeys have provided important data about this issue. The ventral pathway seems to be able to perform complex analyses on several objects simultaneously, but only during a short time period. Subsequently only one or very few objects are explicitly selected and consciously perceived. Here, we survey the implications of these new findings for our understanding of object processing.     

How implicit is visual statistical learning?

In visual statistical learning, participants learn the statistical regularities present in a sequence of visual shapes. A recent study (Kim, Seitz, Feenstra, & Shams, 2009) suggests that visual statistical learning occurs implicitly, as it is not accompanied by conscious awareness of these regularities. However, that interpretation of the data depends on 2 unwarranted assumptions concerning the nature and sensitivity of the tasks used to measure learning. In a replication of this study, we used a 4-choice completion task as a direct measure of learning, in addition to an indirect measure consisting of a rapid serial visual presentation task. Moreover, binary confidence judgments were recorded after each completion trial. This way, we measured systematically the extent to which sequence knowledge was available to consciousness. Supporting the notion that the role of unconscious knowledge was overestimated in Kim et al.'s study, our results reveal that participants' performance cannot be exclusively accounted for by implicit knowledge. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Inspecting visual mental images: Can people “see” implicit properties as easily in imagery and perception?

Can people “see” previously unnoticed properties in objects that they visualize, or are they locked into the organization of the pattern that was encoded during perception? To answer this question, we first asked a group to describe letters of the alphabet and found that some properties (such as the presence of a diagonal line) are often mentioned, whereas others (such as symmetry) are rarely if ever mentioned. Then we showed not only that other participants could correctly detect both kinds of properties in visualized letters, but also that the relative differences in the ease of detecting these two types of properties are highly similar in perception (when the letters are actually visible) and imagery (when the letters are merely visualized). These findings provide support for the view that images can be reinterpreted in ways much like what occurs during perception and speak to the wider issue of the long-standing debate about the format of mental images.     

How position dependent is visual object recognition?

Visual object recognition is often assumed to be insensitive to changes in retinal position, leading to theories and formal models incorporating position-independent object representations. However, recent behavioral and physiological evidence has questioned the extent to which object recognition is position independent. Here, we take a computational and physiological perspective to review the current behavioral literature. Although numerous studies report reduced object recognition performance with translation, even for distances as small as 0.5 degrees of visual angle, confounds in many of these studies make the results difficult to interpret. We conclude that there is little evidence to support position-independent object recognition and the precise role of position in object recognition remains unknown.     

Mental imagery and dyslexia: a deficit in processing multipart visual objects?

Dyslexic and normal control subjects memorized simple line patterns inside a grid and subsequently judged whether an "X" would have fallen on the pattern had it been present in an empty grid. The patterns were letters and novel shapes. The grids were presented to the left visual field, to the right visual field, or in central vision. Dyslexic subjects had difficulty generating images of multipart patterns, but this deficit was limited to letters. The findings suggest that dyslexics may have selective difficulty integrating visual information stored in long-term memory.     

What is primed in priming from imagery?

Priming from imagery is typically weaker than that from perception. This has been interpreted as resulting from weaker activation of perceptual processes. However, for imagery and perception, commonality is only half the story: Each is also characterized by specific processes. If priming can be due to both unshared and shared components of imagery and perception, then it should be possible to observe greater priming from imagery than from perception. Two new priming experiments were designed to test this hypothesis, while controlling incidental task differences. In both experiments, participants studied objects by counting their parts (from a mental image or a picture). Experiment 1 used a word-picture matching test task, which was hypothesized to depend on stimulus processing specific to perception, and Experiment 2 a size judgment test task, which was hypothesized to depend on retrieval and generation processes specific to imagery. As predicted, priming for perceived objects was greater than priming for imagined objects in the word-picture matching task. Conversely, in the size judgment task, more priming from imagery than from perception was observed. These results support the conclusions that (a) imagery and perception have substantial unshared processes, and (b) these processes contribute to priming.     

Why is it difficult to see in the fog? How stimulus contrast affects visual perception and visual memory

Processing visually degraded stimuli is a common experience. We struggle to find house keys on dim front porches, to decipher slides projected in overly bright seminar rooms, and to read 10th-generation photocopies. In this research, we focus specifically on stimuli that are degraded via reduction of stimuluscontrast and address two questions. First, why is it difficult to process low-contrast, as compared with high-contrast, stimuli? Second, is the effect of contrastfundamental in that its effect is independent of the stimulus being processed and the reason for processing the stimulus? We formally address and answer these questions within the context of a series of nested theories, each providing a successively stronger definition of what it means for contrast to affect perception and memory. To evaluate the theories, we carried out six experiments. Experiments 1 and 2 involved simple stimuli (randomly generated forms and digit strings), whereas Experiments 3–6 involved naturalistic pictures (faces, houses, and cityscapes). The stimuli were presented at two contrast levels and at varying exposure durations. The data from all the experiments allow the conclusion that some function of stimulus contrast combines multiplicatively with stimulus duration at a stage prior to that at which the nature of the stimulus and the reason for processing it are determined, and it is the result of this multiplicative combination that determines eventual memory performance. We describe a stronger version of this theory— the sensory response, information acquisition theory—which has at its core, the strong Bloch’s-law-like assumption of a fundamental visual system response that is proportional to the product of stimulus contrast and stimulus duration. This theory was, as it has been in the past, highly successful in accounting for memory for simple stimuli shown at short (i.e., shorter than an eye fixation) durations. However, it was less successful in accounting for data from short-duration naturalistic pictures and was entirely unsuccessful in accounting for data from naturalistic pictures shown at longer durations. We discuss (1) processing differences between short- and long-duration stimuli, (2) processing differences between simple stimuli, such as digits, and complex stimuli, such as pictures, (3) processing differences between biluminant stimuli (such as line drawings with only two luminance levels) and multiluminant stimuli (such as grayscale pictures with multiple luminance levels), and (4) Bloch’s law and a proposed generalization of the concept ofmetamers.     

Subvocalization in auditory-verbal imagery: just a form of motor imagery?

Previous studies have provided evidence for subvocal rehearsal (inner voice) and phonological storage (inner ear) in auditory-verbal imagery. The question remains to be answered whether the inner voice mainly involves higher-order language systems, or primarily relies on motor systems associated with articulatory-kinesthetic processing. On the basis of models of auditory imagery and working memory, we predicted that, if auditory-verbal imagery is a form of motor imagery, performance on a novel auditory-verbal imagery task would be affected by concurrent articulatory suppression as well as by concurrent finger tapping. In contrast, we predicted that performance on a visuospatial control task would be significantly affected by concurrent tapping only. The auditory imagery task consisted of indicating, for bisyllabic words, the syllable that carried the stress. A significant interaction was observed between task (verbal vs. visual) and type of interference (articulatory suppression vs. tapping). Tapping affected reaction times on the visual task significantly more than articulatory suppression. However, both interference conditions affected the verbal task to an equal extent. The present findings confirm the role of subvocalization in auditory-verbal imagery and provide evidence for a strong involvement of articulatory-kinesthetic motor processing.     

How is Christianity Incarnated in Society?

Abstract

This article offers a magisterial survey of the history of Christian interaction with the wider culture. Part of the purpose is to indicate how the current success of charismatic churches is symptomatic of a general pattern of interaction rather than some major digression from it. Arguing that Christianity inserts into culture a repertoire selectively received according to type of social context, the author addresses motifs such as the collective and/or individual Victim, the righteous remnant, the heroic leader or Solomonic king of an elect nation or empire, and the martyr, heretic or dissident arguing that in Jesus the prophet-priest-king motif is combined with the Victim and martyr motif, in such a way as to undermine the sacral unity of religion and empire in successive waves of evangelisation, Pentecostalism being the latest.     

Beyond the qualitative-quantitative divide: How to proceed?

The author addresses three commentaries to his earlier article “On the possibility of contextual-quantitative inquiry.” In response to these commentaries, the author identifies some examples of contextual-quantitative inquiry in use, questions the necessity of a link between numeric data and Pythagoreanism, and argues that not all methodological possibilities can be entertained at once in coherent research. Finally, the author notes that this argument regarding numeric forms of inquiry in contextual-interpretive research attempts to avoid the extremes of uncritical methodological inclusiveness on the one hand and overly narrow methodological exclusiveness on the other.     

Einstein’s jacket: Evidence for long-term perceptual specificity in mental imagery

To what extent are visual fantasies constrained by our perceptual experience of the real world? Our study exploits the fact that people’s knowledge of the appearance of individuals from the early 20th Century (e.g., Albert Einstein, Winston Churchill) derives predominantly from viewing black-and-white media images. An initial experiment shows that mental imagery for individuals from this period are experienced as significantly less colourful than imagery for individuals from the era of colour media. A second experiment manipulated whether participants were instructed to explicitly imagine using colour or not (i.e., “imagine Albert Einstein wearing a green jacket” vs. “imagine Albert Einstein wearing a jacket”). Results show that colour manipulation only influences imagery for black-and-white era individuals, with no comparable effect on imagery for colour era individuals. This finding is replicated in a third experiment that includes an additional control condition of imagining generic characters (i.e., “Imagine a knight wearing a cloak” vs. “imagine a knight wearing a red cloak”). Again, only imagery for black-and-white era individuals is affected by the colour manipulation. Overall these results provide evidence for long-term perceptual specificity effects in mental imagery. We argue that visual fantasies can be constrained by surface features of underlying representations in memory, even when imagining something we have never directly perceived.     

How could phenomenal consciousness be involved in mental function?

In a phylogenetic perspective, the phenomenal and the functional aspects of consciousness cannot be separated because consciousness, as a phenomenal experience, must be causally effective. The hypothesis I propose is that the fundamental property of consciousness consists of a self-organizing process: the differentiation of a content. The differentiation of a content occurs on the basis of the relations internal to a representational whole, which behaves like a field and tends towards a condition of equilibrium. This hypothesis can be somehow considered an extension of Gestalt visual perceptual theory. Unlike neurocomputational processes, which are non-conscious and extrinsic to the representation, conscious processes are intrinsic to the representational whole. Consciousness, as an intrinsically self-organizing process interwoven with its phenomenal aspects, can be more than epiphenomenal and it can be involved in mental function. The paper then discusses the implications of this hypothesis for subjectivity and the explanatory gap.     

What is wrong with imagery questionnaires?

Research evidence is reviewed which shows that the questionnaire method represents a deviant case in imagery research: Whereas experimental techniques consistently produce strong effects for the imagery variable in a large specter of cognitive tasks, research based on imagery questionnaires yields ambiguous and most frequently negative results. Existing explanations of the discrepant findings are critically examined and found to be inadequate. An alternative interpretation is offered, where it is hypothesized that the questionnaire approach to the study of imagery is infected by a serious methodological flaw, due to differences in subjective conceptions of the rating scale employed in imagery questionnaires. Experimental evidence is reported which supports this interpretation.     

Why is visual search superior in autism spectrum disorder?

This study investigated the possibility that enhanced memory for rejected distractor locations underlies the superior visual search skills exhibited by individuals with autism spectrum disorder (ASD). We compared the performance of 21 children with ASD and 21 age‐ and IQ‐matched typically developing (TD) children in a standard static search task and a dynamic search task, in which targets and distractors randomly changed locations every 500 ms, precluding the use of memory in search. Children with ASD exhibited overall faster reaction time (RT) relative to TD children, and showed no disruption in search efficiency in the dynamic condition, discounting the possibility that memory for rejected distractors augments their visual search abilities. Analyses of RT x set size functions showed no group differences in slopes but lower intercepts for the ASD group in both static and dynamic search, suggesting that the ASD advantage derived from non‐search processes, such as an enhanced ability to discriminate between targets and distractors at the locus of attention. Eye‐movement analyses revealed that the ASD and TD groups were similar in the number and spatial distribution of fixations across the search array, but that fixation duration was significantly shorter among children with ASD. Lower intercepts in static search were related to increased symptom severity in children with ASD. In summary, ASD search superiority did not derive from differences in the manner in which individuals with ASD deployed their attention while searching, but from anomalously enhanced perception of stimulus features, which was in turn positively associated with autism symptom severity.     

Imagery experts: How do expert abacus operators process imagery?

This study examined how expert abacus operators process imagery. Without imagery instructions a digit series was auditorily presented as one whole number (WHL list) or separate digits (SEP list). RT from offset of the probe to onset of the response was measured. The main findings were as follows: experts showed no difference in RT between the two lists, while significant differences occurred in non-experts; non-experts' RT increased with probed position, while experts' RT was flat if the series size was within their image capacity; experts' RT increased with probed position when the series size was longer than their image capacity, but its rate of increase was smaller than that of non-experts; and the smaller the image capacity, the steeper the slope of the RT function. It was concluded that experts spontaneously encode the digit series into an imaged abacus, while non-experts encode it verbally; that experts directly access the probed position within their image but serially process the verbally coded overflowed part; and that non-experts search the digit series serially.