Negative affordance effect: automatic response inhibition triggered by handle orientation of non-target object.

Habituated response tendency associated with affordance of an object is automatically inhibited if this affordance cue is extracted from a non-target object. This study presents two go/no-go experiments investigating whether this response control operates in response selection processes and whether it is linked to conflict-monitoring mechanisms. In the first experiment, the participants performed responses with one hand, and in the second experiment, with two hands. In addition, both experiments consisted of two blocks with varying frequency of go conditions (25%-go vs. 75%-go). The non-target-related response inhibition effect was only observed in Experiment 2 when the task required selecting between two hands. Additionally, the results did not reveal patterns typically related to conflict monitoring when go-frequency is manipulated and when a stimulus-response compatibility effect is examined relative to congruency condition of the previous trial. The study shows that the non-target-related response inhibition assists hand selection and is relatively resistant to conflict-monitoring processes.

Sharp and round shapes of seen objects have distinct influences on vowel and consonant articulation.

The shape and size-related sound symbolism phenomena assume that, for example, the vowel [i] and the consonant [t] are associated with sharp-shaped and small-sized objects, whereas [ɑ] and [m] are associated with round and large objects. It has been proposed that these phenomena are mostly based on the involvement of articulatory processes in representing shape and size properties of objects. For example, [i] might be associated with sharp and small objects, because it is produced by a specific front-close shape of articulators. Nevertheless, very little work has examined whether these object properties indeed have impact on speech sound vocalization. In the present study, the participants were presented with a sharp- or round-shaped object in a small or large size. They were required to pronounce one out of two meaningless speech units (e.g., [i] or [ɑ]) according to the size or shape of the object. We investigated how a task-irrelevant object property (e.g., the shape when responses are made according to size) influences reaction times, accuracy, intensity, fundamental frequency, and formant 1 and formant 2 of vocalizations. The size did not influence vocal responses but shape did. Specifically, the vowel [i] and consonant [t] were vocalized relatively rapidly when the object was sharp-shaped, whereas [u] and [m] were vocalized relatively rapidly when the object was round-shaped. The study supports the view that the shape-related sound symbolism phenomena might reflect mapping of the perceived shape with the corresponding articulatory gestures.

Shared processing of planning articulatory gestures and grasping.

It has been proposed that articulatory gestures are shaped by tight integration in planning mouth and hand acts. This hypothesis is supported by recent behavioral evidence showing that response selection between the precision and power grip is systematically influenced by simultaneous articulation of a syllable. For example, precision grip responses are performed relatively fast when the syllable articulation employs the tongue tip (e.g., [te]), whereas power grip responses are performed relatively fast when the syllable articulation employs the tongue body (e.g., [ke]). However, this correspondence effect, and other similar effects that demonstrate the interplay between grasping and articulatory gestures, has been found when the grasping is performed during overt articulation. The present study demonstrates that merely reading the syllables silently (Experiment 1) or hearing them (Experiment 2) results in a similar correspondence effect. The results suggest that the correspondence effect is based on integration in planning articulatory gestures and grasping rather than requiring an overt articulation of the syllables. We propose that this effect reflects partially overlapped planning of goal shapes of the two distal effectors: a vocal tract shape for articulation and a hand shape for grasping. In addition, the paper shows a pitch-grip correspondence effect in which the precision grip is associated with a high-pitched vocalization of the auditory stimuli and the power grip is associated with a low-pitched vocalization. The underlying mechanisms of this phenomenon are discussed in relation to the articulation-grip correspondence.

Contrast discrimination and choice reaction times at near-threshold pedestals.

Choice reaction times (CRTs) to contrast differences were measured and compared with contrast increment thresholds obtained from concurrently measured psychometric functions at pedestal contrasts in the vicinity of detection threshold. Contrast discrimination functions had a classical dipper shape. The main finding was that CRTs were shorter at low pedestal contrasts but longer at higher pedestal contrasts compared to detection, reflecting the behaviour of increment thresholds. Even when equalized for response accuracy, CRTs varied with pedestal contrast in a similar manner to the contrast increment thresholds. The finding that CRTs and contrast increment thresholds depended on pedestal contrast in a similar manner suggests that both share a common origin. This common origin is proposed to lie in the variability of the sensory effect which determines the variability of the information accumulation process, which in turn affects the response criterion and contrast increment thresholds. At low pedestals, a decrease in variability lowers thresholds and results in a lower response criterion, thereby accelerating reaction times. At high pedestals, increasing signal-dependent noise inflates variability and thus raises thresholds and the response criterion, which results in slower CRTs.

Contrast matching across spatial frequencies for isoluminant chromatic gratings.

Contrast matching was performed with isoluminant red-green and s-cone gratings at spatial frequencies ranging from 0.5 to 8 c/deg. Contrast threshold curves were low-pass in shape, in agreement with previous findings. Contrast matching functions resembled threshold curves at low contrast levels, but became flat and independent of spatial frequency at high contrasts. Thus, isoluminant chromatic gratings exhibited contrast constancy at suprathreshold contrast levels in a similar manner as has been demonstrated for achromatic gratings.

Spatial-frequency bandwidth of perceived contrast.

The aim of this study was to investigate the spatial-frequency bandwidth of perceived suprathreshold contrast. It has been shown that for grating stimuli contrast detection thresholds depend on spatial frequency, grating area and the number of orientation components. However, suprathreshold contrast perception exhibits contrast constancy, i.e. suprathreshold contrast matches are independent of these stimulus parameters. To study whether contrast constancy applies to spatial-frequency bandwidth, contrast matching was performed and detection thresholds were measured for spatial noise stimuli at various bandwidths centred at 2 c/deg. At high contrast levels, contrast matches were nearly independent of stimulus spatial-frequency bandwidth up to about 6 octaves, even though detection thresholds increased with bandwidth. Thus, a broad band of spatial frequencies contributed to perceived suprathreshold contrast. The requisites for this are contrast constancy with respect to spatial frequency, and integration of contrast information across different spatial frequencies so that the effective bandwidth of the system is broad.

Contrast restoration model for contrast matching of cosine gratings of various spatial frequencies and areas.

The purpose of the model presented in this paper is to explain the well known fact that perceived contrast becomes independent of optical low-pass and neural high-pass filtering as well as areal integration with increasing stimulus contrast. In the model we assume that perceived contrast is computed by two different parallel mechanisms. One of them integrates signal information across space to improve the signal-to-noise ratio and is affected by the optical low-pass and neural high-pass filtering. The other mechanism estimates external local contrast by using inverse filtering. These two factors are combined by a 'restoration' mechanism so that the first mechanism affects the perception of low contrast and the latter that of high contrast stimuli. The behaviour of the model was tested against experimental results obtained with normal human observers. At low contrast levels, contrast matching curves were similar in shape to the detection threshold curves both as a function of the spatial frequency and area of the grating. At high contrast levels, contrast matches became physically correct. The model described the experimental results accurately.

Contrast matching of two-dimensional compound gratings.

The contrast of a two-dimensional compound grating consisting of 2, 3 or 4 components with the same spatial frequency but different orientations was matched to the contrast of a simple cosine grating. At all spatial frequencies and contrast levels studied the stimuli which matched in apparent contrast had nearly equal r.m.s. (root-mean-square) but different Michelson contrasts. Thus, matching was based on r.m.s. contrast which takes into account the distribution of luminance levels in the stimulus. A matched filter provides a simple model to explain the contrast matching results.

Michelson contrast, RMS contrast and energy of various spatial stimuli at threshold.

Contrast sensitivity was measured as a function of median spatial frequency for vertical cosine gratings, narrow-band noise stimuli, and spots with luminance increment or decrement. Contrast sensitivity was expressed in terms of Michelson contrast, RMS contrast, and contrast energy in order to demonstrate the characteristics of various contrast measures. Gratings and noise stimuli had either constant stimulus area or constant number of cycles. Michelson contrast sensitivity was better for gratings than for noise stimuli or spots, whereas RMS contrast sensitivity was almost equal for gratings and noise stimuli but lowest for spots. Contrast energy sensitivity takes into account the stimulus area and was therefore best for spots.

Effects of luminance and exposure time on contrast sensitivity in spatial noise.

Using gratings with and without spatial noise we measured r.m.s. contrast sensitivity as a function of (i) retinal illuminance, (ii) amount of light added onto the screen, and (iii) exposure time. Our experiments showed that contrast sensitivity in external spatial noise was independent of decreasing retinal illuminance and exposure time as long as contrast sensitivity was lower with noise than without. Thereafter the decrease of contrast sensitivity was identical with and without noise. Although contrast sensitivity without external spatial noise was independent of the amount of added light, contrast sensitivity in external spatial noise was found to increase with the amount of added light until it reached the sensitivity measured without noise. Thereafter contrast sensitivities with and without noise were identical. Our results (i) provide experimental evidence for the validity of the generally accepted hypothesis that in the human contrast detection mechanism signal-to-noise ratio is constant at threshold and (ii) indicate that external spatial noise is the principal source of noise when it reduces contrast sensitivity.