Vision of objects happens faster and earlier for location than for identity

Abstract

Visual perception of objects requires the integration of separate independent stimulus features, such as object identity and location. We ask whether the location and the identity of an object are processed with different efficiency for being consciously recognized and reported. Participants viewed a target letter at one out of several locations that were terminated by pattern masks at all possible locations. Participants reported the location of the target and/or its letter identity. Report performance as a function of the target duration before the mask is enabled to estimate the speed of visual processing and the minimum duration for processing to start. Visual processing was faster and started earlier for spatial location than for object identity, even though the processing of the features was (stochastically) independent. Together, these findings reveal an intrinsic preference of the human visual system for the perceptual processing of space as opposed to visual features such as categorical identity.

Keywords: Cognitive neuroscience; Sensory neuroscience.

Graphical abstract

Figure 1

Paradigm of Experiment 1 After fixating a fixation cross, a single letter target was shown briefly at one out of 12 locations and was followed by pattern masks appearing at all 12 possible locations. At the end of a trial, participants reported the letter identity and the location (the order of these two report types was randomized and counterbalanced across trials).

Figure 2

Results of Experiment 1 (A) Location report performance vs. letter report performance. Points indicate observers’ mean proportion correct, error bars the corresponding 95% confidence intervals for within designs. (B) Observed probabilities of reporting location or letter identity correctly or wrong as a function of the probabilities predicted by the observed marginal probabilities under the assumption of stochastic independence (each point represents one such probability pair for one observer and target duration). The diagonal (dashed) indicates the identity of predicted and observed probabilities (hence stochastic independence), the regression line is shown on top of it in blue. (C) Psychometric function of the aggregate observer for location vs. letter report performance as a function of target presentation duration. Points represent mean proportion correct across observers (with error bars indicating 95% confidence intervals, smooth curves indicate the psychometric functions found by averaging the parameters of the individual observers’ fitted psychometric functions. (D) Means of observers’ temporal perception thresholds and visual processing speed for perceiving location and letter identity, respectively. Error bars provide 95% confidence intervals.

Figure 3

Results of Experiment 2 (A) Psychometric function of the aggregate observer for location vs. letter report performance as a function of target presentation duration. Points represent the mean proportion correct across observers (with error bars indicating 95% confidence intervals³⁷), and smooth curves indicate the psychometric functions found by averaging the parameters of the individual observers’ fitted psychometric functions. (B) Means of observers’ temporal perception thresholds and visual processing speed for perceiving location and letter identity, respectively. Error bars provide 95% confidence intervals.