After-images from retina and brain

The evidence pointing to the retinal origin of after-images is considered. The reports of the occurrence of after-images from visual images of hallucinatory vividness are reviewed.

Experimental results are presented to indicate that a complementarily coloured afterimage may arise following the exposure of the temporarily blind retina to a coloured stimulus.

After-images, or after-effects, from vivid images are described in seventeen persons (mostly possessors of “number-forms”). They are found to move with the eyes and to show, in some persons, a degree of conformity with Emmert's Law which, while considerable, is less than that of after-images of real stimuli. In the case of one “eidetic” subject, the after-images from neither real nor imaged stimuli conformed with Emmert's Law. In some persons, after-images of images occur in complementary colours.

The retinal origin of after-images is affirmed, but that they can occur occasionally as a purely central phenomenon is acknowledged. The possible learned or inherent nature of after-images of central origin is discussed.     

THE LOCUS OF VISUAL AFTER-IMAGES

K olehmainen , K. & T uomisaari , R. The locus of visual after-images. Scand. J. Psychol ., 1969, 10 , 45–48.—Three bright spots of light aligned horizontally were presented, so that the distances between them were equal. Two adjacent lights were flashed on simultaneously and the third one somewhat later. The subjects reported the distance between the midmost light and the light which appeared later to be longer than the distance between the simultaneous lights (the 'tau-effect'). As to the after-images, however, the intervening distances were judged equal. The results are, accordingly, suggestive of a peripheral basis of the after-images.     

Shorter articles and notes: A case of fluctuation of awareness with the pulse

The case is described of a man in whom certain percepts of central origin (after-images of hallucinations) fluctuated rhythmically with the arterial pulse. The phenomenon is explained in terms of contemporary theories of consciousness and the inhibitory effects of baroceptor impulses.

In a previous communication (Oswald, 1957) it was described how some persons may experience visual after-images not only after retinal stimulation but also after the prolonged contemplation of a voluntary vivid image (hallucination). One of those described, Subject Wi, is further discussed below. It is relevant to this case and to the interpretation suggested, to recall that Griffits and Gordon (1924) described the rhythmical increase and decrease of the size, intensity, or apparent distance of vivid images (hallucinations) with rhythmical fluctuations of vasomotor tone, of pulse rate and, by inference, of blood pressure.     

An unusual case of after-imagery following fixation of an “imaginary” visual pattern

The case of a healthy normal subject is described in which negative after-images were reported to follow fixation of an “imaginary” pattern. The size of the after-image was measured at various distances and found to agree closely with the size of an after-image induced by fixation of a “real” visual pattern, and to conform roughly with Emmert's Law. No evidence for chromatic after-images was obtained. Two controls were conducted, one indicating that the results could not be attributed to after-images resulting from objective aids used to maintain an “imaginary” pattern of constant size; the other discounting the possibility of the subject's having guessed the correct values. Similar phenomena reported in the early literature are briefly mentioned, and some theoretical implications discussed.     

The role of central processes in the perception of visual after-images

Three experiments are reported in which part of the stimulus to be after-imaged was presented to each eye, producing simultaneous, binocular, after-images. In each case the monocular stimuli were complementary to each other, so that the binocular combination constituted a meaningful whole. The subjects' reports on the appearances and fragmentations of their after-images suggest the existence of some central, integrative, mechanism.     

Binocular stimulation and the fragmentation of after-images

Two studies were undertaken to investigate the effects of binocular stimulation on the fragmentation of after-images. Binocular after-images were produced by stimulating simultaneously, with intense flashes of light, homologous areas of the two retinas. The after-images from such stimulation were found to be more stable than those produced by monocular stimulation. A third study examined the fragmentation of after-images observed by individuals who either lacked binocular vision and stereoscopic depth perception or who had a history of difficulty with these aspects of vision. Such individuals reported far lass fragmentation than normal observers. The results are discussed in the light of research on the responses to binocular inputs of single cells in monkey occipital cortex.     

Prime-sight and blindsight

Listening to subject's commentaries can be a useful spur to novel scientific departures, as in studies of blindsight. Recently further testing (after a gap of 17 years) has been possible with subject DB, who was a blindsight patient (the first) tested intensively over a period of 10 years and who was the subject of the book, (Blindsight OUP, 1986, 2nd edition, 1998). Essentially his original capacity is the same or somewhat more sensitive. Some further types of discriminations have now been tested that were not possible in the original study. But a new feature was discovered, namely that he describes conscious after-images of a wide range of inducing stimuli of which he is unconscious. The properties of the after-images are briefly described, such as their occurrence following unseen colour patches, luminance changes, shape, spatial frequency, their long durations, showing inter-ocular transfer, as well as their conforming to Emmert's Law. Various approaches are discussed towards finding the source of their generation, such as the use of after-images of colour mixes of separate inputs to the two eyes ("cortical yellow"). They are also discussed in terms of after-images in normal subjects that are generated by imagination. The discovery offers a rare potential opportunity to compare the brain activity associated with both the conscious and unconscious attributes of the precisely the same stimuli in the same locus in the same subject.     

Failures to see: attentive blank stares revealed by change blindness

Change blindness illustrates a remarkable limitation in visual processing by demonstrating that substantial changes in a visual scene can go undetected. Because these changes can ultimately be detected using top-down driven search processes, many theories assign a central role to spatial attention in overcoming change blindness. Surprisingly, it has been reported that change blindness can occur during blink-contingent changes even when observers fixate the changing location [O'Regan, J. K., Deubel, H., Clark, J. J., & Rensink, R. A. (2000). Picture changes during blinks: Looking without seeing and seeing without looking. Visual Cognition, 7, 191-212]. However, eye blinks produce a transient disruption of vision that is independent of any associated changes in the retinal image. We determined whether these 'attentive blank stares' could occur in the absence of blink-mediated visual suppression. Using a flicker change-blindness paradigm we confirm that despite direct attentive fixations, obvious scene changes often remain undetected. We conclude that change detection involves object or feature based attentional mechanisms, which can be 'misdirected' despite the allocation of spatial attention to the position of the change.     

The visual perception of velocity

Summary In this section it is concluded that velocity is perceived directly and is dynamically conditioned by the structure and general properties of the visual field in which the movement occurs. The visual perception of velocity follows dynamic laws that are not immediately deducible from the velocity of the stimulus as physically defined. No physiological theory is offered but it is pointed out that the theory of physiological Gestalten is essentially correct in its basic assumptions concerning the perception of movement.The investigation has bearing on the problems of movement thresholds, movement after-images and the perception of time.This paper is abridged from a thesis presented to the faculty of the graduate school of Yale University in partial fulfilment of the requirements for the degree of Doctor of Philosophy. The study was started in the Psychological Institute of the University of Berlin in 1926–1927 and completed at Yale University in 1928–1929. The work at Berlin, which has been already reported [cf. J. F. Brown, Über gesehene Geschwindigkeit. Psychol. Forschg 10, 84–101 (1927)] was largely exploratory in nature; that at Yale was undertaken to fill the gaps in the experimental series and to control more completely the causal factors. For clarity of exposition the previously reported data are included here so far as necessary. The writer is indebted to Professor W. Köhler of the University of Berlin for suggesting the problem, and to Professors R. P. Angier, R. Dodge, and L. T. Spencer of Yale University for many valuable suggestions. He wishes also to express his thanks to the subjects who served in the experiments.     

When do visual and verbal memories conflict? The importance of working-memory load and retrieval

Examinations of interference between verbal and visual materials in working memory have produced mixed results. If there is a central form of storage (e.g., the focus of attention; N. Cowan, 2001), then cross-domain interference should be obtained. The authors examined this question with a visual-array comparison task (S. J. Luck & E. K. Vogel, 1997) combined with various verbal memory load conditions. Interference between tasks occurred if there was explicit retrieval of the verbal load during maintenance of a visual array. The effect was localized in the maintenance period of the visual task and was not the result of articulation per se. Interference also occurred when especially large silent verbal and visual loads were held concurrently. These results suggest central storage along with code-specific passive storage.     

ATTENTION AND VISUAL IDENTIFICATION TIME

SCHIOLDBORG, P. Attention and visual identification time. Scand. J. Psychol. , 1971, 12 , 289–294.–The identification time of a test object increased when viewed together with other objects, both for central and peripheral identification. When viewed alone, foreknowledge of position facilitated identification in central vision, but not in peripheral vision. A distinction between identification and localization as related to attention is outlined. The results are interpreted in line with a model where focusing and dispersion of attention are regarded as antagonistic processes, implying that the ensuing variation in the momentary attention level for some object affects the amount of information assessed per unit time.     

SUBLIMINAL GRADATION IN THE VISUAL FIELD

K ragh , U. Subliminal gradation in the visual field. Scand. J. Psychol , 1962, 3 , 165–170.—The difference of thresholds for correct recognition of a central figure and of a peripheral figure in the same picture, presented by the tachisto-scope, is referred to two factors: foveal vs . extrafoveal stimulation, and threat towards the central figure (in terms of 'perceptual defense'). Differences of size of the figures, again, do not effect 'subliminal gradation'. The analysis is considered relevant for the comparison between two tachistoscopic techniques: one in which one subliminal stimulus is exposed immediately before a liminal one, and the other with only one subliminal stimulus.     

The contributions of visual and central attention to visual working memory

We investigated the role of two kinds of attention—visual and central attention—for the maintenance of visual representations in working memory (WM). In Experiment 1 we directed attention to individual items in WM by presenting cues during the retention interval of a continuous delayed-estimation task, and instructing participants to think of the cued items. Attending to items improved recall commensurate with the frequency with which items were attended (0, 1, or 2 times). Experiments 1 and 3 further tested which kind of attention—visual or central—was involved in WM maintenance. We assessed the dual-task costs of two types of distractor tasks, one tapping sustained visual attention and one tapping central attention. Only the central attention task yielded substantial dual-task costs, implying that central attention substantially contributes to maintenance of visual information in WM. Experiment 2 confirmed that the visual-attention distractor task was demanding enough to disrupt performance in a task relying on visual attention. We combined the visual-attention and the central-attention distractor tasks with a multiple object tracking (MOT) task. Distracting visual attention, but not central attention, impaired MOT performance. Jointly, the three experiments provide a double dissociation between visual and central attention, and between visual WM and visual object tracking: Whereas tracking multiple targets across the visual filed depends on visual attention, visual WM depends mostly on central attention.     

On the relationship between the redundant signals effect and temporal order judgments: parametric data and a new model

Paradigms used to study the time course of the redundant signals effect (RSE; J. O. Miller, 1986) and temporal order judgments (TOJs) share many important similarities and address related questions concerning the time course of sensory processing. The author of this article proposes and tests a new aggregate diffusion-based model to quantitatively explain both the RSE and TOJs and the relationship between them. Parametric data (13 stimulus onset asynchronies) from an experiment with pairs of visual stimuli (626-nm LEDs) confirm that, relative to central signals (3 degrees), peripheral signals (35 degrees) yield slower reaction times, more strongly modulated RSE time-course functions, and flatter TOJ psychometric functions. All of these qualitative features are well captured, even in quantitative detail, by the aggregate diffusion model.     

Word meaning and the control of eye fixation: semantic competitor effects and the visual world paradigm

When participants are presented simultaneously with spoken language and a visual display depicting objects to which that language refers, participants spontaneously fixate the visual referents of the words being heard [Cooper, R. M. (1974). The control of eye fixation by the meaning of spoken language: A new methodology for the real-time investigation of speech perception, memory, and language processing. Cognitive Psychology, 6(1), 84-107; Tanenhaus, M. K., Spivey-Knowlton, M. J., Eberhard, K. M., & Sedivy, J. C. (1995). Integration of visual and linguistic information in spoken language comprehension. Science, 268(5217), 1632-1634]. We demonstrate here that such spontaneous fixation can be driven by partial semantic overlap between a word and a visual object. Participants heard the word ‘piano’ when (a) a piano was depicted amongst unrelated distractors; (b) a trumpet was depicted amongst those same distractors; and (c), both the piano and trumpet were depicted. The probability of fixating the piano and the trumpet in the first two conditions rose as the word ‘piano’ unfolded. In the final condition, only fixations to the piano rose, although the trumpet was fixated more than the distractors. We conclude that eye movements are driven by the degree of match, along various dimensions that go beyond simple visual form, between a word and the mental representations of objects in the concurrent visual field.     

Double take: parallel processing by the cerebral hemispheres reduces attentional blink

Recent data have shown that parallel processing by the cerebral hemispheres can expand the capacity of visual working memory for spatial locations (J. F. Delvenne, 2005) and attentional tracking (G. A. Alvarez & P. Cavanagh, 2005). Evidence that parallel processing by the cerebral hemispheres can improve item identification has remained elusive. The authors used a novel variant of the attentional blink paradigm to show that the attentional blink is reduced if targets are divided between the hemispheres rather than directed to a single hemisphere. Parallel processing by the cerebral hemispheres can thus expand the capacity of processes involved in item identification. The authors also show that prior engagement of the attentional system may compromise the processing of items directed to the right visual field. This pseudoextinction may explain the failures of previous attempts to demonstrate that parallel processing can improve item identification (J. F. Delvenne, 2005; S. J. Luck, S. A. Hillyard, G. R. Mangun, & M. S. Gazzaniga, 1989).     

The topography of training-induced visual field recovery: Perimetric maps and subjective representations

The cognitive representation of blind regions varies considerably between patients with vision loss and may influence compensatory behaviour and treatment motivation. We therefore measured “objective” visual field topography (perimetry) in 19 patients with postgeniculate visual system lesions and related this to the subjective scotoma representation as expressed by patients’ drawings of the defect and monitored changes of these measures during training-induced recovery of function. Blind regions were mostly adequately represented; however, central regions were overestimated and peripheral areas underestimated in size. Perimetric and subjective defect size decreased significantly during training. Again, training-induced visual field border shifts in central regions were larger in subjective than in perimetric maps but vice versa in the peripheral field. Thus, vision restoration therapy improves “objective” visual field size along with its cognitive representation. The subjective topography is shaped by the functional importance of visual field regions and is a function of cortical magnification, thus resembling the neural representation in visual cortex.     

Nonspatial attentional shifts between audition and vision

This study investigated nonspatial shifts of attention between visual and auditory modalities. The authors provide evidence that the modality of a stimulus (S1) affected the processing of a subsequent stimulus (S2) depending on whether they shared the same modality. For both vision and audition, the onset of S1 summoned attention exogenously to its modality, causing a delay in processing S2 in a different modality. That undermines the notion that auditory stimuli have a stronger and more automatic alerting effect than visual stimuli (M. I. Posner, M. J. Nissen, & R. M. Klein, 1976). The results are consistent with other recent studies showing cross-modal attentional limitation. The authors suggest that such cross-modal limitation can be produced by simply presenting S1 and S2 in different modalities and that central processing mechanisms are also, at least partially, modality dependent.     

PIAGET'S CONCEPT OF SPATIAL EGOCENTRISM: AREEVALUATION

Kielgast, Knud. Piaget's concept of egocentrism: A reevaluation. Scand. J. Psychol. , 1971, 12, 179–191. – It was found that the so-called egocentric reaction of identifying one's own perspective with the imagined perspective of some object seen from a different point of view could not be attributed to a fixation to one's own perspective but rather to a deficient perceptual differentiation between the visual world and the visual field. A comparison of verbal and non-verbal solutions was found to point to a near relationship between perception and imagination in this specific task.     

A NOTE ON INTEROCULAR TRANSFER AND THE COLOUR OF VISUAL AFTER-IMAGES

Following monocular fixation of a red stimulus figure on a grey background, a projection field having the same colour as the stimulus figure was viewed either with ( a ) the stimulated eye, or ( b ) the non-stimulated eye. In case ( a ) the after-image appeared grey on a red background, but in case ( b ) green or blue, on a red background. In the latter case the brightness and to some extent the hue of the after-image varied when the amount of light coming to the originally stimulated eye varied. The data are in agreement with the assumption that after-images are primarily retinal.