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.

Electrophysiological Correlates of the Effect of Task Difficulty on Inhibition of Return.

Inhibition of return (IOR) refers to slower responses to targets that occur at a previously attended location than to those at control locations. Previous studies on the impact of task difficulty on IOR have shown conflicting results. However, these studies failed to match low-level characteristics of stimuli (e.g., size, color, and luminance) across difficulty levels, and so might have confounded the effect of task difficulty with that of stimulus characteristics. Hence, whether and how task difficulty modulates IOR remain largely unknown. This study utilized the event-related potentials (ERPs) technique in combination with a cue-target paradigm to tackle this question. Task difficulty was manipulated by changing the position of a gap in a rectangle stimulus, while stimulus size, color, and luminance were precisely matched. IOR was observed in reaction times across all difficulty levels but was found in accuracy at the medium level only. The modulation effect of task difficulty on IOR was also evident in the N1 and P2 ERP components, which showed significantly weaker IOR effects at the medium difficulty level than at the easy and hard levels. It is suggested that the modulation of IOR by task difficulty involves both perceptual and post-perceptual processes.

The Time Course of Inhibition of Return: Evidence from Steady-State Visual Evoked Potentials.

Inhibition of return (IOR) refers to slower responses to targets at a previously cued location than that at an uncued location. The time course of IOR has long been a topic of interest in the field. Investigations into the time course of IOR are typically performed by examining the magnitude of IOR under various cue-target onset asynchrony (CTOA) conditions. Therefore, the results are vulnerable to influence of factors that could affect the target processes (e.g., the frequency of the target type). In the present study, steady-state visual evoked potentials (SSVEPs) were implemented to directly take a continuous measurement of the degree to which cued location is processed, eliminating the influence mentioned above. The results indicate that, relative to the baseline interval (-400 to 0 ms), the presence of peripheral cues generated a typical two-stage effect on the SSVEP amplitude evoked by a 20 Hz flicker. Specifically, after the onset of the peripheral cues, the SSVEP amplitude first showed a significant increase, which subsequently turned into a significant inhibition effect after 200 ms. These results provide a continuous time course diagram of the cueing effect and suggest an effective way for future investigations of controlling the masking effects of target stimuli processing on IOR.