A consumer-grade LCD monitor for precise visual stimulation

Because they were used for decades to present visual stimuli in psychophysical and psychophysiological studies, cathode ray tubes (CRTs) used to be the gold standard for stimulus presentation in vision research. Recently, as CRTs have become increasingly rare in the market, researchers have started using various types of liquid-crystal display (LCD) monitors as a replacement for CRTs. However, LCDs are typically not cost-effective when used in vision research and often cannot reach the full capacity of a high refresh rate. In this study we measured the temporal and spatial characteristics of a consumer-grade LCD, and the results suggested that a consumer-grade LCD can successfully meet all the technical demands in vision research. The tested LCD, working in a flash style like that of CRTs, demonstrated perfect consistency for initial latencies across locations, yet showed poor spatial uniformity and sluggishness in reaching the requested luminance within the first frame. After these drawbacks were addressed through software corrections, the candidate monitor showed performance comparable or superior to that of CRTs in terms of both spatial and temporal homogeneity. The proposed solution can be used as a replacement for CRTs in vision research.     

The Extended Maxwellian View (BIGMAX): A high-intensity,high-saturation color display for clinical diagnosis and vision research

We describe a device that can display very high intensity (up to 400,000 cd/m²), high-resolution visual stimuli. The device is inexpensive, is easily controlled by a conventional computer and video card, and can be calibrated for use in vision research or clinical applications. The display is capable of presenting highly saturated, near spectral colors. Unlike Maxwellian view optical systems, our display can be viewed binocularly and does not require exacting head restraint. We describe the construction, give a design example, and describe our calibration procedure. Furthermore, we report measurements of the color gamut, spatial resolution, temporal characteristics, and the dynamic range of light intensity.     

Unconscious vision and executive control: How unconscious processing and conscious action control interact

Research on unconscious or unaware vision has demonstrated that unconscious processing can be flexibly adapted to the current goals of human agents. The present review focuses on one area of research, masked visual priming. This method uses visual stimuli presented in a temporal sequence to lower the visibility of one of these stimuli. In this way, a stimulus can be masked and even rendered invisible. Despite its invisibility, a masked stimulus if used as a prime can influence a variety of executive functions, such as response activation, semantic processing, or attention shifting. There are also limitations on the processing of masked primes. While masked priming research demonstrates the top-down dependent usage of unconscious vision during task-set execution it also highlights that the set-up of a new task-set depends on conscious vision as its input. This basic distinction captures a major qualitative difference between conscious and unconscious vision.     

Discounting mechanism underlies extinction illusion

Humans can perceive a coherent visual scene despite a low spatial resolution in peripheral vision. How does the visual system determine whether an object exists in the periphery? We addressed this question by focusing on the extinction illusion in which a disk becomes subjectively invisible when presented at the intersection of grids. We hypothesized that the disk would go unnoticed when the stimuli with and without the disk produced the same strength of visual signals. The visual system would miss the disk by confounding the target signals with the intersection signals that should be discounted. Computational analysis revealed that the energy ratio between the stimuli with and without the disk decreased with stimulus eccentricity and such energy ratio could successfully explain the observer’s d’ to detect the disk. These results indicate that the discounting mechanism relying on stimulus energy determines the awareness toward a peripheral object.     

Tachistoscopic software for the Macintosh

The emulation of a tachistoscope with a Macintosh microcomputer and Pascal language is presented here. The software described is a complete program for the presentation of textual stimuli on the Macintosh screen and includes the recording of reaction times. The stimulus coordinates on the screen are user defined and variable from trial to trial for specific visual angles. The position of a fixation point on the screen and the distance between the subject and the plane of the screen, as well as the particular screen resolution, are taken into account in computing the visual angle.     

Emotion-induced trade-offs in spatiotemporal vision

It is generally assumed that emotion facilitates human vision in order to promote adaptive responses to a potential threat in the environment. Surprisingly, we recently found that emotion in some cases impairs the perception of elementary visual features (Bocanegra & Zeelenberg, 2009b). Here, we demonstrate that emotion improves fast temporal vision at the expense of fine-grained spatial vision. We tested participants' threshold resolution with Landolt circles containing a small spatial or brief temporal discontinuity. The prior presentation of a fearful face cue, compared with a neutral face cue, impaired spatial resolution but improved temporal resolution. In addition, we show that these benefits and deficits were triggered selectively by the global configural properties of the faces, which were transmitted only through low spatial frequencies. Critically, the common locus of these opposite effects suggests a trade-off between magno- and parvocellular-type visual channels, which contradicts the common assumption that emotion invariably improves vision. We show that, rather than being a general "boost" for all visual features, affective neural circuits sacrifice the slower processing of small details for a coarser but faster visual signal.     

Projecting two words with one machine: Presenting two different visual stimuli using just one projector without viewers’ noticing the duality

A new method, named the fMORI technique, for presenting two different visual stimuli using just one video projector without the viewers' noticing the duality is introduced along with several sample applications of this presentation method. The LCD projectors available now have three color LCD panels aligned differently in terms of their polarization, polarizing differently the green and magenta (red plus blue) components of its emitting image. Therefore, two visual stimuli either in green or in magenta projected on thesame screen canbe observed separately by subjects wearing an appropriate polarizing filter. This is a variation of the MORI technique (Mori, 2003, 2007b) but it requires only one video projector rather than two. Full-color movies cannot be presented with the fMORI technique, but it may be utilized in various research areas in which only static monochrome visual stimuli, such as words or numbers, are used.     

Box for interaction with objects (BIO): A new device to synchronize the presentation of objects with electrophysiological recordings

Brain event-related potentials are a useful tool for investigating visual processing and action planning. This technique requires extremely accurate synchronization of stimulus delivery with recordings. The precision of the onset time of visual stimulus delivery is a major challenge when attempting to use real, three-dimensional objects as stimuli. Here, we present an innovative device, the “box for interaction with objects” (BIO), that is designed to synchronize the presentation of objects with electroencephalographic (EEG) recordings. To reach the required resolution of stimulus-onset timing, the BIO system features an interface with reflective glass and light-emitting diodes (LEDs). When the LEDs inside the BIO are turned on, the object inside becomes visible, and a synchronizing pulse is sent to the recording systems. The BIO was tested in a motivational study that focused on visual and motor event-related potentials. EEG signals were recorded during the presentation of an emotion-laden object that could be grasped and brought close to the participant’s chest. BIO successfully synchronized the appearance of a three-dimensional object with EEG recordings, which would allow for an analysis of visual and motor event-related potentials in the same experiment. The BIO device, through a high-quality psychophysiological approach, offers a new perspective for the study of the motivational factors that drive actions toward relevant stimuli.     

Picture Perception Lab: A program for picture perception experiments on the Macintosh II

Picture Perception Lab (PPL) is a program for picture perception experiments. PPL capitalizes on the sophisticated drawing software available for the Macintosh computer by allowing the user to create stimulus images by using almost any drawing package. Through a series of user-friendly dialog boxes, PPL enables even nonprogrammers to develop, quickly and easily, tachistoscopelike vision experiments. The program allows a wide variety of experimental designs. Image exposure durations and subjects’ reaction times are precisely monitored with millisecond timing functions. Each image is drawn on the screen in a single 60-Hz refresh.     

The role of the magnocellular visual pathway in the attentional blink

Visual attention has temporal limitations. In the attentional blink (AB) a stream of stimuli such as letters or digits are presented to a participant on a computer monitor at a rapid rate. Embedded in the stream are two targets that the participant must try to identify. Identification of the second target is severely impaired if it is presented within approximately 500ms of the first target. This is the 'blink' in visual attention. In this study we examined the role of the magnocellular visual pathway in the AB. This fast conducting pathway has high temporal resolution and contrast sensitivity. It is also insensitive to the direction of chromatic contrast, and this attribute was exploited in order to isolate its contributions to temporal attention. Colour defined, luminance noise masked AB streams were compared to AB streams of varying achromatic contrast. The four observers, (2F and 2M) aged between 21 and 35years, had normal visual acuity and colour vision. The colour stimuli produced a similar blink to the moderate contrast achromatic stimuli. This indicates that the magnocellular pathway does not have a privileged role in the attentional blink. We provide an explanation of previous apparently contradictory findings in terms of the role of different types of visual masking in the attentional blink.     

Emotions Evoked by Viewing Pictures may Affect Temporal Aspects of Visual Processing

We examined how impression (such as safety, pleasantness, and impact), as well as emotional arousal and valence, evoked by viewing a picture affects temporal resolution of visual processing and perceived picture duration. In the first experiment as an index of temporal resolution of visual processing, we measured the noticeable duration of a monochrome picture after presenting a color picture. In the second experiment, we measured the duration of the picture presentation, which was equivalent to the duration of the presentation of a gray rectangle that should not evoke specifically safe or pleasant impressions. We found that the minimum duration in which an observer could notice a monochrome image in viewing a dangerous picture was shorter than that in viewing safe pictures. We also found that observers overestimated the duration of the picture presentation in viewing dangerous pictures. However, there was no significant correlation between the results of the two experiments. These results suggest that the basis for improvement of the temporal resolution in visual processing differs from that for the elongation of the perceived duration.     

Hand position alters vision by biasing processing through different visual pathways

The present study investigated the mechanisms responsible for the difference between visual processing of stimuli near and far from the observer's hands. The idea that objects near the hands are immediate candidates for action led us to hypothesize that vision near the hands would be biased toward the action-oriented magnocellular visual pathway that supports processing with high temporal resolution but low spatial resolution. Conversely, objects away from the hands are not immediate candidates for action and, therefore, would benefit from a bias toward the perception-oriented parvocellular visual pathway that supports processing with high spatial resolution but low temporal resolution. We tested this hypothesis based on the psychophysical characteristics of the two pathways. Namely, we presented subjects with two tasks: a temporal-gap detection task which required the high temporal acuity of the magnocellular pathway and a spatial-gap detection task that required the spatial acuity of the parvocellular pathway. Consistent with our prediction, we found better performance on the temporal-gap detection task and worse performance on the spatial-gap detection task when stimuli were presented near the hands compared to when they were far from the hands. These findings suggest that altered visual processing near the hands may be due to changes in the contribution of the two visual pathways.     

Full-screen ultrafast video modes over-clocked by simple VESA routines and registers reprogramming under MS-DOS

Fast full-screen presentation of stimuli is necessary in psychological research. Although Spitczok von Brisinski (1994) introduced a method that achieved ultrafast display by reprogramming the registers, he could not produce an acceptable full-screen display. In this report, the author introduces a new method combining VESA routine calling with registers reprogramming that can yield a display at 640 × 480 resolution, with a refresh rate of about 150 Hz.     

Attentional resolution

Attention can enhance selectively the visual information processing of particular locations or objects. Recent studies have shown that this enhancement has limited spatial resolution, the smallest regions that can be isolated by attention are much coarser than the smallest details that can be resolved by vision. Multiple similar objects spaced more finely than the limit of attentional resolution cannot be individuated for further processing and can only be perceived as a grouped texture. As a result, at any given time, only part of the spatial and temporal information registered by the early sensory systems is available to conscious perception. It is likely that attentional resolution is limited at a stage beyond V1 and that it has a finer grain in the lower visual field than in the upper field. The spatial aperture of attention is elongated along the radial axis relative to fixation. The briefest temporal window of attention is also much broader than visual temporal resolution. Many perceptual phenomena related to rapid serial visual presentation may reflect the limited temporal resolution of attention.     

Flooding therapy: Effectiveness,stimulus characteristics,and the value of brief in vivo exposure

Three analogue experiments examined flooding therapy. Experiment 1 showed that flooding was more effective than standardized desensitization in reducing snake phobia. Experiment 2 examined three different modes of presenting the feared stimuli in flooding: taped auditory presentation, pictorial presentation, and a combination of these two. An additional combination group were given a brief in vivo exposure to the feared object immediately after each of three treatment sessions. Both a behavioral test and subjective estimates of fear showed advantages for the combined group that had the in vivo exposure, although it appeared that auditory instructions to imagine interaction with the snake was the best method for presenting the feared stimuli. Experiment 3 compared the auditory imagined method with and without ‘aversive’ or ‘implosive’ scenes, and with either an immediate or a delayed in vivo exposure. The only procedure to produce marked effects was the one that omitted ‘aversive’ scenes and provided immediate post-treatment in vivo exposure.     

The dynamic-stimulus advantage of visual symmetry perception

It has been speculated that visual symmetry perception from dynamic stimuli involves mechanisms different from those for static stimuli. However, previous studies found no evidence that dynamic stimuli lead to active temporal processing and improve symmetry detection. In this study, four psychophysical experiments investigated temporal processing in symmetry perception using both dynamic and static stimulus presentations of dot patterns. In Experiment 1, rapid successive presentations of symmetric patterns (e.g., 16 patterns per 853 ms) produced more accurate discrimination of orientations of symmetry axes than static stimuli (single pattern presented through 853 ms). In Experiments 2-4, we confirmed that the dynamic-stimulus advantage depended upon presentation of a large number of unique patterns within a brief period (853 ms) in the dynamic conditions. Evidently, human vision takes advantage of temporal processing for symmetry perception from dynamic stimuli.     

Attention to repeated events in human infants (Homo sapiens): effects of joint visual attention versus stimulus change

The goal of this study was to examine the effect of joint visual attention on infants' behavior during subsequent events. Thirty-seven mother-infant (aged from 9 to 13 months) pairs were twice shown a pair of line drawing stimuli on a computer screen. For the control group, the mother never paid attention to the stimuli. For experimental group 1, the mother pointed to one stimulus in the first presentation but did not point to it in the second presentation. The infants gazed longer at the stimulus pointed to by their mothers in the first presentation. In the second presentation, during which mothers did not attend to the stimuli, infants gazed longer at the stimulus which had been pointed to by the mothers in the first presentation. In experimental group 2, one of two stimuli blinked during the first presentation but not the second presentation. Infants gazed for longer at the blinking stimulus in the first presentation, but there was no difference in looking time toward the two stimuli in the second presentation. These results suggest that joint visual attention affects infants' looking behavior during subsequent events, and that simple stimulus change does not. Accepted after revision: 2 May 2001 Electronic Publication     

计算机控制心理学实验过程的计时误差分析

计算机在控制心理学实验过程中,可能引入各种潜在的计时误差,特别在短时呈现各种实验刺激时,有些误差是不应忽略的。本文重点分析屏幕刷新率对实验设计的限制及可能产生的计时误差和解决方法。     

Real-time color-frame animation for visual psychophysics on the Macintosh computer

Psychophysical experiments involving moving stimuli require the rapid presentation of animated sequences of images. Although the Macintosh computer is widely used as a color graphics computer in research laboratories, its animation capabilities are generally ignored because of the speed limitations of drawing to the screen. New off-screen color graphics structures help to avoid the speed limitations so that real-time color or gray-scale visual motion stimuli may be generated. Precomputed animation frames are stored in off-screen memory and then rapidly transferred to the screen sequentially. The off-screen graphics structures may also be saved to disk in “Picture” form as “resources” for later retrieval and playback, allowing the experimenter to build in advance a collection of moving stimuli to use in future experiments. Code examples in the C programming language are provided, and the relative strengths and weaknesses of Macin-tosh color-frame animation for psychophysical experimentation are discussed.     

Mantra: an open method for object and movement tracking

Mantra is a free and open-source software package for object tracking. It is specifically designed to be used as a tool for response collection in psychological experiments and requires only a computer and a camera (a webcam is sufficient). Mantra is compatible with widely used software for creating psychological experiments. In Experiments 1 and 2, we validated the spatial and temporal precision of Mantra in realistic experimental settings. In Experiments 3 and 4, we validated the spatial precision and accuracy of Mantra more rigorously by tracking a computer controlled physical stimulus and stimuli presented on a computer screen.