Anna Brooks

Hands as sex cues: sensitivity measures, male bias measures, and implications for sex perception mechanisms.

Sex perceptions, or more particularly, sex discriminations and sex categorisations, are high-value social behaviours. They mediate almost all inter-personal interactions. The two experiments reported here had the aim of exploring some of the basic characteristics of the processes giving rise to sex perceptions. Experiment 1 confirmed that human hands can be used as a cue to an individual’s sex even when colour and texture cues are removed and presentations are brief. Experiment 1 also showed that when hands are sexually ambiguous observers tend to classify them as male more often than female. Experiment 2 showed that “male bias” arises not from sensitivity differences but from differences in response biases. Observers are conservative in their judgements of targets as female but liberal in their judgements of targets as male. These data, combined with earlier reports, suggest the existence of a sex-perception space that is cue-invariant.

An illusion of coherent global motion arising from single brief presentations of a stationary stimulus

We describe a new illusion in which a single stationary stimulus appears to undergo coherent global motion. Contrast relationships between the stimulus elements suggest the illusion arises via processing of Off- and On-channel signals that remain independent until after passing through low-level motion detectors. We propose that patterns of activation resulting from biphasic temporal impulse response functions in the magnocellular pathway are the basis of the illusion, and describe a model to account for the illusory motion percept.

The role of ON- and OFF-channel processing in the detection of bilateral symmetry

We present evidence that grouping for luminance does not take precedence over the detection of bilaterally symmetrical patterns. Using single-axis and double-axis images, we found that element pairs within which luminance is held constant drive symmetry-detection mechanisms more effectively than pairs within which luminance varies. Moreover, the performance decrement observed for patterns defined by element pairs within which luminance varies is not specific to interchannel variation. Luminance variation within the ON and OFF channels has the same effect as variation between the channels on the performance of axis-orientation identification tasks. It is argued that this constitutes possible evidence for subchannels within the ON and OFF channels. One of the characteristics of the subchannels is that each processes only a limited range of luminance steps. The implications of this type of luminance processing for the detection of symmetry in the visual scene are discussed.

Masking the sound induced flash illusion

There is evidence that visual concomitants of articulation facilitate speech perception. Specifically, the results of a study examining Cantonese phone and tone discrimination showed that Australian non-tonal language speakers were able to discriminate phones (consonants and vowels) on the basis of rigid head motion alone. Conversely, neither rigid head motion nor non-rigid face motion alone was sufficient for the visual perception of tones. However, participants in this experiment were non-tone language speakers with normal hearing. If visual information for tone is a general language phenomenon, augmentation may be graded in terms of familiarity of attending to visual cues. Thus, in order to determine the nature of the visual concomitants of tone, research needs to be conducted with people experienced in attending to visual cues. The aim of the present study was to explore the relationship between rigid and non-rigid head motion and the perception of phones and tones by using a hearing impaired population. An experiment was designed using Cantonese words to explore the visual concomitants of phones and tones across three different modalities (Audio Only, Visual Only and Auditory Visual) and three movement types (rigid, non-rigid, and combined). Preliminary results indicate the existence of visual information for phones and tones.When a single flash of a visual stimulus is accompanied by two auditory beeps, the single flash is perceived as two flashes. This is the sound induced flash illusion. A growing body of evidence suggests that the auditory information influences visual processing very early in the visual processing pathway, perhaps in V1 (e.g. Mishra, Martinez, Terrence, Sejnowski & Hillyard; 2007, Watkins, Shams, Tanaka, Haynes & Rees; 2006). We have recently demonstrated targets that selectively and coherently drive the M-pathway, such as a high contrast flashed disc, result in a strong illusion (van der Zwan, Cottrell, Brooks, & Reid; 2007). In the reported experiment we followed up these findings by testing the hypothesis that the illusion depends, to a large extent, activity in the M-pathway. We presented he illusion inducing stimuli flanked by either a forward or backward visual mask at either short (50ms) or long (200ms) SOA. The illusion remained strong in all but the forward masking condition at the short SOA. We argue that this finding is consistent with the illusion being dependent on activity in the ON and OFF channels of the M-pathway.