Effects of band-pass spatial frequency filtering of face and object images on the amplitude of N170.

Previous studies have suggested that physiological responses are greatest and face recognition performance is best when a band of middle relative spatial frequencies (SFs) is included in stimuli. Conversely, behavioural data suggest that object recognition performance shows comparatively little effect of SF variations. Here, we examine the effects of SF filtering on the amplitude of the N170 ERP component when participants are shown images of faces and objects. Our findings show that with face stimuli the amplitude of N170 exhibits a band-pass modulation function, with responses to middle SFs (around 11 cycles per face) being statistically indistinguishable from responses to full-band faces. In contrast to faces, object stimuli elicited a relatively flat function across much of the spectrum. However, for both faces and objects, middle spatial frequencies were sufficient to elicit the same N170 magnitude as full-band images. Our results with face stimuli are in accordance with previous work examining single-cell and MEG responses. Our results with objects are compatible with previous behavioural work showing a relative robustness of object recognition to SF manipulations. Our findings are novel in showing that the middle band elicits the same N170 as full-band images in both faces and objects.

Spatial vision meets spatial cognition: examining the effect of visual blur on human visually guided route learning.

Visual navigation is a task that involves processing two-dimensional light patterns on the retinas to obtain knowledge of how to move through a three-dimensional environment. Therefore, modifying the basic characteristics of the two-dimensional information provided to navigators should have important and informative effects on how they navigate. Despite this, few basic research studies have examined the effects of systematically modifying the available levels of spatial visual detail on navigation performance. In this study, we tested the effects of a range of visual blur levels--approximately equivalent to various degrees of low-pass spatial frequency filtering--on participants' visually guided route-learning performance using desktop virtual renderings of the Hebb-Williams mazes. Our findings show that the function of blur and time to finish the mazes follows a sigmoidal pattern, with the inflection point around +2 D of experienced defocus. This suggests that visually guided route learning is fairly robust to blur, with the threshold level being just above the limit for legal blindness. These findings have implications for models of route learning, as well as for practical situations in which humans must navigate under conditions of blur.

Inhibition of return for the discrimination of faces.

When a target appears unpredictably in the same rather than a different location relative to a preceding onset cue, reaction times (RTs) of participants tasked with responding to the target are slowed. This pattern of results, referred to as inhibition of return (IOR), is believed to reflect the operation of a mechanism that prevents perseverative search of nontarget locations. On the grounds that an evolved mechanism might be sensitive to social stimuli, Taylor and Therrien (2005) examined IOR for localization responses under conditions in which cues and targets could be intact face configurations or nonface configurations; contrary to their predictions, there was no influence of cue or target configuration on the magnitude of IOR, indicating that the mere occurrence of task-irrelevant face and nonface stimuli does not alter IOR. In the present study, we further examined this issue in a task that required a face/nonface target discrimination. When target configuration was thereby made task relevant, we found that IOR differed for face and nonface targets in terms of magnitude (when a single cue-target stimulus onset asynchrony was employed) and time course. We suggest that the RT delay associated with IOR may enable additional processing time and/or response selection when a task-relevant face is presented at the cued location.

Inhibition of return for faces.

Inhibition of return (IOR) refers to slower reaction times when a target appears unpredictably in the same location as a preceding cue, rather than in a different location. In the present study, frontal images of human faces were presented intact as face configurations, were rearranged to produce scrambled-face configurations, or were pixilated and randomized to produce nonface configurations. In an orienting paradigm designed to elicit IOR, face and scrambled-face stimuli were used as cues (Experiment 1), as targets (Experiment 2), or along with pixilated nonface stimuli as both cues and targets (Experiment 3). The magnitude of IOR for subsequent localization targets was unaffected by cue configuration. Likewise, the magnitude of IOR was unaffected by target configuration. These results suggest that IOR is a "blind" mechanism that is unaffected by the mere occurrence of biologically relevant cue and target stimuli.