[Effects of contrast, eccentricity and position in the detection of visual stimuli in humans]. / Efectos del contraste, excentricidad y posicion en la deteccion de estimulos visuales en humanos.

INTRODUCTION: Contrast, eccentricity and position of stimuli used on research of attention in human vision strongly vary among studies. AIM. To study how contrast, eccentricity and position affects detection of stimuli in humans. SUBJECTS AND METHODS: In adults with normal vision, we measured response times to stimuli (gray circles of 0.5 masculine of diameter) presented at random at eight polar coordinates, in three eccentricities with respect of fixation point (2.15, 3.83 and 5.53 masculine) and with three levels of contrast (6, 16 and 78%). RESULTS: Stimuli with eccentricity of 5.38 masculine and 6% of contrast showed the longest response times. In all eccentricities studied, longer response times were found with stimuli of 6% of contrast. Response times of stimuli of 16% and 78% of contrast showed similar response times in all eccentricities studied. Response times founded at eight polar coordinates were heterogeneous at eccentricities of 2.15 and 5.53 masculine, but not at 3.83 masculine. CONCLUSIONS: Contrast is the factor that most influence detection of visual stimuli used in this study, particularly at the biggest eccentricity employed. Response times among polar coordinates are also affected by eccentricities of 2.15 and 5.53 masculine, suggesting that distance of stimuli to fixation point is critical for visual detection of stimuli.

Efectos del contraste, excentricidad y posición en la detección de estímulos visuales en humanos / Effects of contrast, eccentricity and position in the detection of visual stimuli in humans

Introducción. Los estudios en humanos sobre percepción visual espacial tienen en común proyectar estímulos en laretina central, pero difieren notablemente en cuanto a su contraste, excentricidad y posición en el campo visual. Objetivo. Estudiar los efectos del contraste, excentricidad y posición en la detección de estímulos visuales presentados en la retina central humana. Sujetos y métodos. Se estudiaron los tiempos de respuesta, en personas con visión normal, a la presentación de estímulos (círculos grises de 0,5º de diámetro) presentados al azar en ocho coordenadas polares, con tres excentricidades (2,15,3,83 y 5,53º) y tres niveles de contraste (6, 16 y 78%). Resultados. Los estímulos presentados a 5,53º de excentricidad y contraste del 6% mostraron los tiempos de respuesta más elevados. Con este contraste, los tiempos de respuesta fueron mayores en todaslas excentricidades estudiadas. Por el contrario, con contrastes del 16 y 78%, los tiempos de respuesta fueron similares en las tres excentricidades. Para las ocho coordenadas polares, los tiempos de respuesta fueron homogéneos en la excentricidad de 3,83º y mostraron mayor variabilidad en las excentricidades de 2,15 y 5,53º. Conclusiones. De los tres factores analizados,el contraste es determinante en la detección de estímulos, especialmente en la excentricidad mayor. La posición también influye cuando los estímulos se presentan con excentricidades pequeñas o grandes, lo que sugiere que la distancia de los estímulos respecto al punto de fijación es crítica en la detección visual en este tipo de estudios

Introduction. Contrast, eccentricity and position of stimuli used on research of attention in human vision strongly vary among studies. Aim. To study how contrast, eccentricity and position affects detection of stimuli in humans. Subjects and methods. In adults with normal vision, we measured response times to stimuli (gray circles of 0.5º of diameter) presented at random at eight polar coordinates, in three eccentricities with respect of fixation point (2.15, 3.83 and 5.53º) and with three levels of contrast (6, 16 and 78%). Results. Stimuli with eccentricity of 5.38º and 6% of contrast showed the longest response times. In all eccentricities studied, longer response times were found with stimuli of 6% of contrast. Response times of stimuliof 16% and 78% of contrast showed similar response times in all eccentricities studied. Response times founded at eight polar coordinates were heterogeneous at eccentricities of 2.15 and 5.53º, but not at 3.83º. Conclusions. Contrast is the factor thatmost influence detection of visual stimuli used in this study, particularly at the biggest eccentricity employed. Response times among polar coordinates are also affected by eccentricities of 2.15 and 5.53º, suggesting that distance of stimuli to fixationpoint is critical for visual detection of stimuli