$model->attributes['name']['first'];

$model->attribute['name']['first']

public function setNameFirstAttribute($value)
{
    $this->attributes['name']['first'] = $value;
}

public function getNameFirstAttribute($value)
{
    return "First name : " . $value;
}

public function getNameAttribute($value)
{
    $first = $this->getAttribute("name.first");
    $last = $this->getAttribute("name.last");

    return $first . ' ' . $last;
}