Christian Graff

Human ability to detect kinship in strangers' faces: effects of the degree of relatedness

The resemblance between human faces has been shown to be a possible cue in recognizing the relatedness between parents and children, and more recently, between siblings. However, the general inclusive fitness theory proposes that kin-selective behaviours are also relevant to more distant relatives, which requires the detection of larger kinship bonds. We conducted an experiment to explore the use of facial clues by ‘strangers’, i.e. evaluators from a different family, to associate humans of varying degrees of relatedness. We hypothesized that the visual capacity to detect relatedness should be weaker with lower degrees of relatedness. We showed that human adults are capable of (although not very efficient at) assessing the relatedness of unrelated individuals from photographs and that visible facial cues vary according to the degree of relatedness. This sensitivity exists even for kin pair members that are more than a generation apart and have never lived together. Collectively, our findings are in agreement with emerging knowledge on the role played by facial resemblance as a kinship cue. But we have progressed further to show how the capacity to distinguish between related and non-related pairs applies to situations relevant to indirect fitness.

Firstborns’ Disadvantage in Kinship Detection

The ability to assess genetic ties is critical to defining one’s own family and, in a broader context, to understanding relationships in groups of strangers. To recognize younger siblings as such, human firstborns can rely on the perinatal association of the mother with her new baby. Later-borns, who cannot rely on such an association, will by necessity actuate alternate strategies, such as recognition of facial clues set aside by firstborns. The effects of such differential early experiences deserve consideration; the development of matching abilities may be used throughout an individual’s lifetime to detect other kinship types outside the family. In simple cognitive tasks based on matching face pictures, later-borns surpassed firstborns in detecting kinship among strangers; this pattern was found in populations of different ages and in two countries. This birth-order effect contrasts with the traditional cognitive advantage of firstborns. Inclusive fitness theory explains how early life history promotes specific strategies that can, in turn, permanently enhance human performance in certain domains.

Navigating from a Depth Image Converted into Sound

Background. Common manufactured depth sensors generate depth images that humans normally obtain from their eyes and hands. Various designs converting spatial data into sound have been recently proposed, speculating on their applicability as sensory substitution devices (SSDs). Objective. We tested such a design as a travel aid in a navigation task. Methods. Our portable device (MeloSee) converted 2D array of a depth image into melody in real-time. Distance from the sensor was translated into sound intensity, stereo-modulated laterally, and the pitch represented verticality. Twenty-one blindfolded young adults navigated along four different paths during two sessions separated by one-week interval. In some instances, a dual task required them to recognize a temporal pattern applied through a tactile vibrator while they navigated. Results. Participants learnt how to use the system on both new paths and on those they had already navigated from. Based on travel time and errors, performance improved from one week to the next. The dual task was achieved successfully, slightly affecting but not preventing effective navigation. Conclusions. The use of Kinect-type sensors to implement SSDs is promising, but it is restricted to indoor use and it is inefficient on too short range.

Spontaneous eye-blinking rate from pre-term to six-months

Abstract Little is known about the development of eye blinking, a spontaneous activity mediated by dopamine, from the period in utero to six months after birth. We evaluated spontaneous eye blinking rates (SBR) for 11 full-term and 11 premature infants with their mothers. Dyads were videotaped during bottle-feeding in natural context: at birth, at term (for premature infants), three months, and six months after term. Infants’ and mothers’ blinks were counted in a double-blind procedure. Premature infants blinked over six times more than fetuses of similar maturational age recorded in utero in the previous literature. SBR (around two blinks per minute) show no visible increase over the next six months, and no difference between the pre-term and typical groups. Infants’ rates contrasted with those of their mothers (around five blinks per minute) who were thus recorded under the same conditions. Our longitudinal and ecological record confirms previous results showing low blinking rates of infants before one year. It illustrates the importance of delivery in the expression of a spontaneous behavior. It defines the typical early stage of a behavior that develops later in relation with the dopaminergic system and speech.

Prototyping and Evaluating Sensory Substitution Devices by Spatial Immersion in Virtual Environments

Various audio-vision Sensory Substitution Devices (SSDs) are in development to assist people without sight. They all convert optical information extracted from a camera, into sound parameters but are evaluated for different tasks in different contexts. The use of 3D environments is proposed here to compare the advantages and disadvantages of not only software (transcoding) solutions but also of hardware (component) specifics, in various situations and activities. By use of a motion capture system, the whole person, not just a guided avatar, was immersed in virtual places that were modelled and that could be replicated at will. We evaluated the ability to hear depth for various tasks: detecting and locating an open window, moving and crossing an open door. Participants directed the modelled depth-camera with a real pointing device that was either held in the hand or fastened on the head. Mixed effects on response delays were analyzed with a linear model to highlight the respective importance of the pointing device, the target specifics and the individual participants. Results are encouraging to further exploit our prototyping set-up and test many solutions by implementing e.g., environments, sensor devices, transcoding rules, and pointing devices including the use of an eye-tracker.

Blinking when talking depends on the receiver: The case of mothers feeding infants

Abstract During nursing, a mother faces an infant who does not speak and hardly blinks. We established the eye-blinking rate in this special interactive context for comparison with the high rate repeatedly reported in between adult conversation. The 22 mothers we observed during bottle-feeding blinked much less—especially when talking to their infant—than when talking with another adult. Nursing may have put mothers in a state of concentration that inhibits blinking. So, we propose that the frequent blinks usually displayed during conversations may depend on intentions or expectations about the receiver, which maybe modulated by the affective state.