研究目的
Investigating the feasibility of using Landolt C optotypes with a P300 acuity paradigm and assessing the relationship between subjective and objective acuity estimates for both optotype and grating stimuli.
研究成果
The study demonstrated the feasibility of obtaining objective acuity estimates with optotype stimuli using the P300 component of event-related potentials. P300-based estimates of acuity showed the same discrepancy between optotype and grating stimuli as do the psychophysical measurements, providing a perspective for meaningful objective acuity estimation in visual disorders that differentially affect grating and optotype acuity.
研究不足
The study acknowledges the relatively low number of trials per condition, resulting from the large number of conditions that were to be compared, which reduced the signal-to-noise ratio. Additionally, the prediction intervals for the Landolt C stimuli were relatively large, indicating potential variability in the results.
1：Experimental Design and Method Selection:
The study used dioptric blur to degrade vision and separate oddball sequences with Landolt Cs and gratings to record the P300. Thresholds were estimated by fitting a sigmoid curve to P300 amplitudes as a function of Landolt C size or grating coarseness. Psychophysical thresholds were also obtained for both stimulus types.
2：Thresholds were estimated by fitting a sigmoid curve to P300 amplitudes as a function of Landolt C size or grating coarseness. Psychophysical thresholds were also obtained for both stimulus types.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: Twelve subjects participated in each of the two experiments, with four subjects participating in both. All participants had no known disorders of the visual or neural system.
3：List of Experimental Equipment and Materials:
A Philips GD403 CRT monitor was used for stimulus presentation. EEG was recorded with a 32-channel EEG system with actiCAP active electrodes (BrainAmp; Brain Products, Gilching, Germany).
4：Experimental Procedures and Operational Workflow:
Stimuli were presented for 493 ms with an interstimulus interval of 493 ms. Landolt C optotypes in six different sizes and gratings of six different spatial frequencies were used as infrequent stimuli among frequent stimuli. Subjects were instructed to silently count one of the two orientations of the infrequent stimuli.
5：Data Analysis Methods:
The EEG data were analyzed offline using interactive software (Igor Pro; Wavemetrics, Lake Oswego, OR, USA). P300 magnitude was estimated from the maximum ERP amplitude in the 200- to 700-ms interval of the response difference. Sigmoid functions were fitted to describe the P300 amplitude as a function of the size of the critical detail.
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