Low-level Cues Research Articles

Face-gender discrimination is possible in the near-absence of attention.

The attentional cost associated with the visual discrimination of the gender of a face was investigated. Participants performed a face-gender discrimination task either alone (single-task) or concurrently (dual-task) with a known attentional demanding task (5-letter T/L discrimination). Overall performance on face-gender discrimination suffered remarkably little under the dual-task condition compared to the single-task condition. Similar results were obtained in experiments that controlled for potential training effects or the use of low-level cues in this discrimination task. Our results provide further evidence against the notion that only low-level representations can be accessed outside the focus of attention.

Interaction of top-down and bottom-up processing in the fast visual analysis of natural scenes

The influence of task requirements on the fast visual processing of natural scenes was studied in 14 human subjects performing in alternation an “animal” categorization task and a single-photograph recognition task. Target photographs were randomly mixed with non-target images and flashed for only 20 ms. Subjects had to respond to targets within 1 s. Processing time for image-recognition was 30–40 ms shorter than for the categorization task, both for the fastest behavioral responses and for the latency at which event related potentials evoked by target and non-target stimuli started to diverge. The faster processing in image-recognition is shown to be due to the use of low-level cues, but source analysis produced evidence that, regardless of the task, the dipoles accounting for the differential activity had the same localization and orientation in the occipito-temporal cortex. We suggest that both tasks involve the same visual pathway and the same decisional brain area but because of the total predictability of the target in the image recognition task, the first wave of bottom-up feed-forward information is speeded up by top-down influences that might originate in the prefrontal cortex and preset lower levels of the visual pathway to the known target features.

Velocity constancy in a virtual reality environment.

During everyday life the brain is continuously integrating multiple perceptual cues in order to allow us to make decisions and to guide our actions. In this study we have used a simulated (virtual reality--VR) visual environment to investigate how cues to speed judgments are integrated. There are two sources that could be used to provide signals for velocity constancy: temporal-frequency or distance cues. However, evidence from most psychophysical studies favours temporal-frequency cues. Here we report that two depth cues that provide a relative object--object distance--disparity and motion parallax--can provide a significant input to velocity-constancy judgments, particularly when combined. This result indicates that the second mechanism can also play a significant role in generating velocity constancy. Furthermore, we show that cognitive factors, such as familiar size, can influence the perception of object speed. The results suggest that both low-level cues to spatiotemporal structure and depth, and high-level cues, such as object familiarity, are integrated by the brain during velocity estimation in real-world viewing.

Auditory facilitation: Procedural or sensory effect?

A few studies have reported that, under certain conditions, thresholds following exposure to a sound may be lower than those measured without prior stimulation. For example, Rubin [J. Acoust. Soc. Am. 32, 670-681 (1960)] found a 7-dB negative shift in threshold, for a 20-ms tone presented 160 ms after termination of a low-level cue tone. This "auditory facilitation" was obtained with an up-and-down psychophysical method. In the present study, auditory facilitation was reexamined using an adaptive, two-interval, two-alternative-forced-choice (2I, 2AFC) procedure. Thresholds were measured for 20-ms tones at 1 and 5 kHz, preceded by a 15-dB SL 80-ms cue tone of the same frequency. In addition, thresholds were measured with the cue absent. The results show that thresholds can be lower in the presence of the cue than in its absence, but the effect averages 0.5 dB or less and seems to be independent of cue-signal delay between 80 and 640 ms. Because this finding contrasts with the 7-dB facilitation, which Rubin obtained using an up-and-down method, part of his experiment was replicated and the results were essentially the same as his. The failure to find a pronounced facilitation effect with a 2I, 2AFC procedure indicates that the poststimulatory lowering of threshold found by Rubin primarily resulted from biases and criterion shifts.

Sensitivity to latent cues as a function of 2 changes in skin resistance: orienting response and basal drop.

A test of sensitivity to low-level cues is described. The test consists of 32 pairs of items; one of each pair is similar, in some specific way, to a standard stimulus. Basal skin resistance was monitored continuously during each subject's performance. Sensitivity to a particular item was significantly related to subjective confidence on that item and to increase in relaxation during the judgment period for that item (change in basal skin resistance), and negatively related to an orienting response to that item. Implications for therapeutic sensitivity are discussed.